What's that sound?

[TsherryUSA]

Let's play "What's! That! Sound?!"

I started hearing this sound after a camping trip this past summer. I recall driving over / kicking out a small rock while parking on gravel.

Vehicle:1999 Ford Explorer OHV 5-Speed Manual with ~103k miles

The situation: It is a rapid-fire, machine gun growling sound coming from the front of the vehicle. It can be felt through the floorboards at times. Sometimes it lasts less than 1 second, other times it spans up to 3 seconds. This sound happens only while the vehicle is moving. It happens at any speed, but typically occurs while moving through 30 mph. It occurs in gear, in neutral, in gear - clutch depressed, and while braking. It can occur on smooth pavement, or sometimes is triggered by a bump in the road.

I put together a compilation of the sound from this morning's drive: If the link doesn't work, please tell me and I'll upload to youtube and repost the link.
https://photos.app.goo.gl/XruAyhro15ZvRcg48

What I've done so far: When this sound initially occurred, the ABS light came on. I took it to the mechanic and they diagnosed a bad rear speed sensor, but was unable to replicate the noise. I replaced the rear speed sensor myself. Later, I replaced the both front speed sensors while doing the front brakes. Issue is still occurring.

I'm not opposed to taking to the mechanic, but I'd like to be able to point them in the right direction. Don't want another "unable to replicate problem" diagnostic that I have to pay for.

Thoughts?

Thank you!

 

[rustylugnut]

Sounds almost like something is rubbing on the tire to me. Possibly something plastic. I'd look closely at the inner fender and such, to see if the airflow could be pushing anything into the tire.

 

[TsherryUSA]

Sounds almost like something is rubbing on the tire to me. Possibly something plastic. I'd look closely at the inner fender and such, to see if the airflow could be pushing anything into the tire.

Thanks for the reply. I went back and took a look around there. Everything is solid with plenty of clearance to the tire. Wish it had been that simple, but good to do due diligence.

 

[EB4X]

A gremlin with a small jack hammer under your hood ?
What did I win for guessing correctly ?!?

 

[Mountinheer]

Different size tires? Can really make ABS system angry.

 

[TsherryUSA]

Different size tires? Can really make ABS system angry.

Not the tires. That was the first upgrade when I bought the vehicle. I am thinking it is something to do with the ABS. Maybe it is a bad hub and that is causing the ABS to fire? The sound does not appear to affect driving performance or gas mileage.

I rocked the wheels back and forth last time I had the vehicle raised and didn't see any play though.

@EB4X , Good guess, but I hit the undercarriage with a liberal application of "Grem-Deet" when I bought the vehicle.

 

[Mountinheer]

If brake pedal gets stiff during noise, it's almost certainly the abs pump running because it thinks the wheels are running different speeds... if you are sure the tires are all same size, and replaced rear sensor already - i would change front sensors (or maybe one is just loose).

 

[J_C]

When my ABS fires it doesn't sound like that, but supposing that needs to be ruled out, you can pull the ABS fuse to prevent it from engaging, but ABS shouldn't be activating at all if you aren't braking, even if there is a hub or speed sensor issue.

At first I was wondering if you had a speed mismatch causing 4WD to kick in but you have the AWD instead so that can't be it.

You can also use an OBD2 scan tool that shows the wheel sensor speeds in real time, for example an ELM327 dongle with Forscan app. It may also be able to pull the ABS code if the ABS light is on.

You might still want to inspect the tires for abnormal wear or a significant difference in tire pressure, but given the ABS codes you may be onto something about it being a bad hub.

You could try pulling the speed sensors and wiping them off, and rotating the hub while using a small brush to get any grease loaded with metal contaminants out of the sensor ring teeth (if any is visible). If you use a code scanner then instead of doing both you can focus on the specific wheel.

However on my '98, I first started getting the sensor fault causing ABS activation at very low speeds (under 10MPH) not 30MPH and more often when turning while braking, and never when not braking.

I'd pull the ABS fuse first. Quick & easy way to rule out ABS if it still makes the noise without ABS getting power. Its fuse location should be in your owner's manual.

 

[fast_dave]

@TsherryUSA

Just askin' - On your AWD Ex, do you rotate your tires every 5,000 miles?

 

[974X4BLACKSPORT]

Sounds like the engine cooling fan rubbing the fan shroud, or loose fan shroud rubbing the engine fan.

 

[rustylugnut]

Doesn't sound like ABS to me. Doesn't hurt to pull the fuse and rule it out for sure though.
Doesn't sound like a hub either. Could be the cooling fan. Is the sound wheel speed or rpm dependent? Try to raise the rpm while the noise is present to determine that.
Could be in the suspension. Seems like it creates a pretty hefty vibration through the body. The way it happens after hitting bumps reminds me of "death wobble" in vehicles with a solid front axle. Does it get worse if you hit the brakes/step on the gas?

 

[TsherryUSA]

First off, thanks for all the great replies. I appreciate everyone playing this silly game and helping me out get my EX diagnosed.

If brake pedal gets stiff during noise, it's almost certainly the abs pump running because it thinks the wheels are running different speeds... if you are sure the tires are all same size, and replaced rear sensor already - i would change front sensors (or maybe one is just loose).

I put in new front sensors the last time I did brake pads, so those should be good.

When my ABS fires it doesn't sound like that, but supposing that needs to be ruled out, you can pull the ABS fuse to prevent it from engaging, but ABS shouldn't be activating at all if you aren't braking, even if there is a hub or speed sensor issue.

At first I was wondering if you had a speed mismatch causing 4WD to kick in but you have the AWD instead so that can't be it.

You can also use an OBD2 scan tool that shows the wheel sensor speeds in real time, for example an ELM327 dongle with Forscan app. It may also be able to pull the ABS code if the ABS light is on.

You might still want to inspect the tires for abnormal wear or a significant difference in tire pressure, but given the ABS codes you may be onto something about it being a bad hub.

You could try pulling the speed sensors and wiping them off, and rotating the hub while using a small brush to get any grease loaded with metal contaminants out of the sensor ring teeth (if any is visible). If you use a code scanner then instead of doing both you can focus on the specific wheel.

However on my '98, I first started getting the sensor fault causing ABS activation at very low speeds (under 10MPH) not 30MPH and more often when turning while braking, and never when not braking.

I'd pull the ABS fuse first. Quick & easy way to rule out ABS if it still makes the noise without ABS getting power. Its fuse location should be in your owner's manual.

I'll give the ABS fuse a test tomorrow. The problem sound is usually made within the first minute of driving, so shouldn't take to long to find out if that's the case. I have the torque app + OBD2 plug, but it looks like that doesn't do individual wheel speed. I'll check out Forscan. If not, maybe time to invest in a irl OBD2.

On another note, would driving it with 4WD High switched on be a good test? If the problem relates to it trying to kick 4WD on while I'm in AWD mode, then that theoretically wouldn't happen if I'm in 4WD high. Totally dry road conditions here right now though.

@fast_dave , good question. I'm due for a rotation. Problem began occurring when tires were very fresh though, so I don't think it's that.

Sounds like the engine cooling fan rubbing the fan shroud, or loose fan shroud rubbing the engine fan.

I'll add it to the list of things to check! Thanks!

Doesn't sound like ABS to me. Doesn't hurt to pull the fuse and rule it out for sure though.
Doesn't sound like a hub either. Could be the cooling fan. Is the sound wheel speed or rpm dependent? Try to raise the rpm while the noise is present to determine that.
Could be in the suspension. Seems like it creates a pretty hefty vibration through the body. The way it happens after hitting bumps reminds me of "death wobble" in vehicles with a solid front axle. Does it get worse if you hit the brakes/step on the gas?

I have noticed that when it occurs while braking, the sound slows. I haven't noticed the opposite when accelerating, but that may be because the noise interval is often very short and an increase in revs is more difficult to hear for whatever reason.

Thanks again everyone. I really appreciate it.

 

[Mountinheer]

Ok, now I bet on front hubs.

 

[J_C]

On another note, would driving it with 4WD High switched on be a good test? If the problem relates to it trying to kick 4WD on while I'm in AWD mode, then that theoretically wouldn't happen if I'm in 4WD high. Totally dry road conditions here right now though.

You listed your vehicle as AWD. Is it AWD or 4WD? AWD comes with the 5.0L V8 engine. 4WD has the mode selector switch on the dash.

If you have 4WD then no, you should not put a 4WD in 4WD mode and drive around on dry roads, except in a straight line. If you find a straight stretch of road where you don't have to go very fast and the problem occurs, you could temporarily switch a 4WD into 4hi to see if that stops the noise but take it back out of 4hi before making any turns. To be clear if you have 4WD you can put it in 4hi on the fly while driving and disengage while driving.

 

[EB4X]

To be clear if you have 4WD you can put it in 4hi on the fly while driving and disengage while driving.

Interesting...wasn't aware of this....so this would apply to my 'first year' of second gen '95 model as well.....correct?
And while on topic of "4 hi" it's my understanding it's safe to drive in that up to say 50 MPH...is this correct? Posted a while back on this and don't recall detailed response....

 

[TsherryUSA]

You listed your vehicle as AWD. Is it AWD or 4WD? AWD comes with the 5.0L V8 engine. 4WD has the mode selector switch on the dash.

If you have 4WD then no, you should not put a 4WD in 4WD mode and drive around on dry roads, except in a straight line. If you find a straight stretch of road where you don't have to go very fast and the problem occurs, you could temporarily switch a 4WD into 4hi to see if that stops the noise but take it back out of 4hi before making any turns. To be clear if you have 4WD you can put it in 4hi on the fly while driving and disengage while driving.

That was a mistake on my part. I thought the first option on the selector switch has was "AWD". It is in fact, "AUTO". I have the 4WD 4.0L MFI OHV V6 Explorer.

Took the ABS cabin fuse out this AM on a short errand. Problem noise still occurred. I'll try the ABS fuse under the hood next just in case that is different. Didn't have time today to get to that.

Reading through the manual, it talks about the ABS performing a test at 10mph when just driving. Could this be the system performing a test at other speeds? No steering wheel shake though.

Interesting...wasn't aware of this....so this would apply to my 'first year' of second gen '95 model as well.....correct?
And while on topic of "4 hi" it's my understanding it's safe to drive in that up to say 50 MPH...is this correct? Posted a while back on this and don't recall detailed response....

The owners manual for my 1999 EX states this, so maybe check there first.

 

[J_C]

I never noticed mine performing that test at all, even when I had my ABS problem below 10MPH coming to stops because of the wheel sensor.

If you took the passenger compartment fuse out, that should have disabled ABS so now I would not consider it a possible suspect.

 

[Elessar65]

The ABS pump cycles a lot faster than that, I don't think its ABS related. I would be more inclined to believe it has to do with the transfer case.

 

[rustylugnut]

Disable the tcase operation by yanking the fuse. Not sure exactly how its controlled on these older trucks but I'd imagine theres one for a 4wd module and at least one for the tcase.

 

[J_C]

Interesting...wasn't aware of this....so this would apply to my 'first year' of second gen '95 model as well.....correct?
And while on topic of "4 hi" it's my understanding it's safe to drive in that up to say 50 MPH...is this correct? Posted a while back on this and don't recall detailed response....

I know that in the '96 owner's manual, it mentions it can be shifted on the fly and it also has the 2WD/4WD Auto/4WD Low selector switch that changes on later model year 2nd gen's. I would assume this is also true for a '95 but don't know it for certain.

However the manual also states "Because of possible damage to drivetrain components, never shift from two-wheel drive to 4WD with the rear wheels
slipping", so while it is on the fly, you shouldn't do it at the very moment you'd really need it.

50MPH seems like a sensible limit but I don't recall if I've ever seen any statement from Ford about the max speed in 4WD HI, while the max in 4lo is 10MPH. I have read about people continuously exceeding 50MPH in 4hi without causing any immediate damage but people do all sorts of things they aren't supposed to and get away with it, so you make your choices and take your chances.