Trying to Diagnose A Noise
 

My 2001 4.4 has had an unusual "whirring" noise for a few months now. At first I thought it was a tire going bad. Than I thought wheel bearing. I have had it jacked up, pushed and pulled on numerous parts of suspension. Wheels on, wheels off, no clunks or discernible unusual noises. It sounds like the rear, but could be front. Considered the front diff. Changed the oil, everything seems fine. Now, turning wheel suddenly to the right while driving lessens the noise for a moment. So, it's driving me nuts and slowly getting worse. Anyone have any suggestions on how to diagnose a bad wheel bearing? My next step is to jack it up, all 4 wheels off the ground and run it to listen more closely. Want to fix this before it goes on me while driving. Any help would be appreciated.

Bad wheel bearings are hard to pin down and they usually drone more than they whir.

On the E53 a bad wheel bearing will make a LOT of noise long before it fails completely. They are double races (two ball races in parallel) and so it can be hard to locate a bad bearing based on wheel movement - even with a failed bearing, the wheel doesn't move much. AMHIK...

A whirring might be the power steering pump?

Try driving on a clear road at about the speed you hear the noise/sound. Gently turn the steering a few degrees to the left and then the right. A noisy/faulty bearing that gets unloaded will get quiet. When turning the wheel to the left, the left side is unloaded and turning to the right, the right side is unloaded. See if you have any differential in sound doing this and it may give you an indicator.

Can you record it?

The best way to determine wheel bearing is to put on a different width tire eg usually 255 then switch to 235. It swaps the forces from toe in top to toe out top and swaps the forces on the races it will make a dramatic change in the drone. Since you don't know which way the wheel is being forced (in or out) it's impossible to know for example when you turn left or right, are you adding or subtracting force from the inner or outer race, but put a skinny wheel on and your are guaranteed to flip the forces. (I found that out the hard way when I lent my wife my 255s and on some 245 spares I had and instantly my car started to drone like a plane from a 1960s war movie. Change one tire at a time to the 235 spare and see if you get a dramatic change (quieter or louder).

tires
 

Thanks for the input. The diagnosis is the hardest part of this. I do have snow tires that I will need to put on. Is putting a smaller tire on one corner ok for the differential(s)?? I always thought this was a major issue. I tried recording the noise today, but it isn't discernible enough.