Low roar or pitched hum or whine

[Sixonemale]

I have a 2002 4x4 Explorer and recently had the back differential fluid changed about two months ago and also had new tires put on it at about the same time. It has about 138,000 miles on it.

Recently I have notice a low roar hum when driving, especially slowing down from about 40 mph. I initially thought it was the tires and had them rotated, did not help. I then thought it was the front right wheel bearing/hub assembly, drivers side and had it replaced, but the noise is still there. I also took it to a transmission shop and they listen for noise around the differential, but could not conclude nor say the noise was coming from the differential. It's not a horrible noise, but it is something that was never there before and makes me think that this is a short distance vehicle for the time being.

Any thoughts of where this noise may be coming from or how to diagnose it would be greatly appreciated. Thanks

 

[Ronin8002]

Could be a loose pinion nut which would result in the pinion gear getting deflected while coasting AKA gear whine. You can tell by unbolting the driveshaft and seeing if there's any play in the yoke on the diff.

 

[M1911A1]

I have a 2002 4x4 Explorer and recently had the back differential fluid changed about two months ago and also had new tires put on it at about the same time. It has about 138,000 miles on it.

Recently I have notice a low roar hum when driving, especially slowing down from about 40 mph. I initially thought it was the tires and had them rotated, did not help. I then thought it was the front right wheel bearing/hub assembly, drivers side and had it replaced, but the noise is still there. I also took it to a transmission shop and they listen for noise around the differential, but could not conclude nor say the noise was coming from the differential. It's not a horrible noise, but it is something that was never there before and makes me think that this is a short distance vehicle for the time being.

Any thoughts of where this noise may be coming from or how to diagnose it would be greatly appreciated. Thanks

You describe three different characteristic noises on your heading; if it's a "humming" sound, as if you're riding on heavy snow tires over dry surfaces, it's most likely wheel bearing issues. If it "roars" or "whines" I would consider rear differential/yoke issues. Have you check the rear diff. fluid level? I would be inclined to suspect bad bearings. Sometimes it helps to let someone else drive the car on a quiet hwy. while you ride seating on different angles of the truck, with the windows down. Have the driver change lanes to try to discern different tones or lack of noise while the weight is shifted off the different bearings. Good luck.

 

[maryland1966]

This year Explorer is known to have rear end problems and the whine is just the beginning. It's a $1000 + repair. It could be the rear wheel bearing (another costly repair) but the rear diff will go out sooner rather than later.

 

[Sixonemale]

You describe three different characteristic noises on your heading; if it's a "humming" sound, as if you're riding on heavy snow tires over dry surfaces, it's most likely wheel bearing issues. If it "roars" or "whines" I would consider rear differential/yoke issues. Have you check the rear diff. fluid level? I would be inclined to suspect bad bearings. Sometimes it helps to let someone else drive the car on a quiet hwy. while you ride seating on different angles of the truck, with the windows down. Have the driver change lanes to try to discern different tones or lack of noise while the weight is shifted off the different bearings. Good luck.

I'm thinking too it is a wheel bearing problem, so I may have to have the other three checked, perhaps one in the back is bad. I had a transmission expert take a stethoscope device the truck and he could not say definitively that it was the differential or wheel bearing. As a matter of fact he thought differential was probably fine, and this is a guy who could have made money to fix it. His advice was to wait till it gets worse, since to him it was so subtle.

The Ford dealer also could not diagnose it and thought it was the differential beginning to go bad.

When I start up the car and drive it initially, the noise is not that pronounced, but after a mile or two I can really hear the noise when I slow down from 40 mph and lower. It's low pitched, almost rubbing like noise. I initially thought it was my tires, then thought maybe a brake malfunction of some sort, but am probably back to the wheel bearing, possibly one of the back wheels.

Is it an easy diagnoses to take off the wheels and spin the wheel hub/bearing assembly and be able to tell whether it's worn out or not?

 

[TThomason]

I have replaced the wheel bearings in the rear of my 2002 ford explorer, oh also the shocks and the rear springs, seems like the 02 have these problem, oh I forgot to mention the trans mission also, $4,000. for it.

 

[cmyers2220]

I have replaced 2 of my bearings, both rear springs, and a remanufactured trannny at $3300.
The humming I am getting too. After I let off the gas it seems to quiet a bit. I think someone said in another thread it may be the differential getting noisy? But I think they said changing the fluid won't help. Replacing that will be very expensive I bet.

 

[Sixonemale]

I have replaced 2 of my bearings, both rear springs, and a remanufactured trannny at $3300.
The humming I am getting too. After I let off the gas it seems to quiet a bit. I think someone said in another thread it may be the differential getting noisy? But I think they said changing the fluid won't help. Replacing that will be very expensive I bet.

I keep going back and forth from thinking it's the differential or the wheel bearings. I think mine did the same thing yesterday, when I let off the gas it was quiet. I don't think there is an easy way to diagnose this, but from what you written, it does sound like it could be differential.

 

[RickM]

I keep going back and forth from thinking it's the differential or the wheel bearings. I think mine did the same thing yesterday, when I let off the gas it was quiet. I don't think there is an easy way to diagnose this, but from what you written, it does sound like it could be differential.

Under load the Rear diff will be noisy on the 2002-2005 Exps. Just about everyone here reports this unfortunate condition. Only one that I can recall had one grenade of them though. When replacing rear diff oil go with the Ford recommended, higher viscosity synthetic oil. I also added Lucas oil stabilizer as well. So far it's helped quite a bit.

New, replacement rear wheel bearings will also contribute to the symphony of rear-end sounds, especially if not pressed perfectly straight into the hub. Low quality, aftermarket bearings wont help either.