Whining Noise

[Steved80]

I tried looking thru the site to see if something like this was posted already, but i am not finding it. Just recently a whining noise has started with my explorer. It only happens when it is in gear and moving. It is a faint sound that sounds like a siren starting up that gets higher pitch as you go faster. The tranny was just rebuilt about 2 years ago, maybe 30,000 miles at most, so i don't think it is that. It shifts fine as well. It does not do it when in park or neutral which makes me think it is not power steering or water pump. When in drive or reverse but with the brake on so not moving it does not make the sound either. both front wheel bearings have been replaced recently as well as the front differential. It sounds like it is from the front, but i know sounds can travel in a car. I am thinking it is some bearing, but not sure which one it could be. Maybe driver line? Anyone have this happen before? Any other ideas of what to check and how?

 

[Explorer_PL]

Unfortunately, there are at least 10 places it can be coming from if not more.
What I do is put the car on 4 safe stands or supports so I have all 4 wheels in the air.
I sometimes use a bar/stick to lock the steering wheel in 1 position.
Select 4x4, press the traction control button and hold it for 5 sec until it flashes, then release it.
I then put the car in D, jam a piece of wood between the driver seat and the gas pedal and get it to the speed when you hear the noise., and go under and listen to the bearings, transfer case, both differentials.
Just the transfer case has 3-4 places it can have bad bearing.
Very common failure is the front of the front u-joint, inexpensive part, about $ 20. It was making that type of noise on mine.
I also had a rear output bearing failure in my transfer case, and it sounded like wheel bearings as well.
Do not discount the rear bearings even if you think it's coming form the front.
Do all above at your own risk or have a shop do it on the lift.

 

[Steved80]

Thanks for the info. Was hoping to at least narrow it down to bearings of some sort, and not something else. A good place to start at least. For rear wheel bearings, would they change in sound when turning like the front wheel bearings, or since they don't turn would it just be the same no matter what? I am considering just taking it in to put on a lift, but would like to have some idea of what is going on so i can make sure it is getting addressed correctly.