I know this is difficult to answer, and maybe I just shouldn't ask over the internet.

Above 40 MPH, a sound resonates that seems to originate from the rear end...it is not constant, but does seem to be speed related (lower freq with lower speed and slightly higher freq as vehicle speed increases - wha wha wha .... wha wha wha - seems to be most pronounced off the straight away).

Below 40 MPH - nothing, at stop in Drive - nothing, in park - nothing.

I've replaced the tires - no change.

Just drained and refilled the differential - no change in noise - although some have told me to get rid of the 90/140 oil my garage just put in there.

Can I rule-out a torque-tube problem? Is a bad wheel bearing most likely cause?

I have after-market 17-inch rims, but don't see any signs of tire rubbing the wells...

Thanks for any assist!

Mike (wha wha wha...)

 

I had a simular issue and it turned out to be the tires. I believe if it is a wheel bearing the pitch is suppose to change during a corner. I'm sure someone more experienced will chime in but it sounds like tire noise to me.

 

Goes away on turns left or right? Wheel Bearing issue.
Clunk sound? Look at the U-Joint Boots
Vibrations? Look at the ball joints in the rear.
Did brakes lately? Loose Caliper

 

I don't think it's a bearing noise. That's more of a growl. That noise increases with speed and if bad enough can be felt through the floor board. Noise increases when turning to the opposite side that the bearing is on.

Is it a noise and vibration, or just noise?

 

Wheel bearing noise will change as you go around sweepers ( freeway on ramps ) at speed. The outside wheel loads up the inside unloads...more noise when loaded tells you which side if it is a wheel bearing. Is your car a 5spd speed or sutomatic ?

 

Mine is an 87 automatic with LSD. Sound seems to be most prevalent through turns (as when entering an on or off-ramp). And the sound is never constant - it doesn't persist, but comes and goes - only change is with its pitch and I only hear it above 40 MPH - not very loud, but notable.

A typical duration might be wha wha wha wha wha...goes away...comes back...goes away. I sound silly.

Watched a couple guys on you-tube diagnose a bad wheel bearing by jacking the wheel up and checking for unusual play - I might as well check myself.

Mike

 

The style of wheel bearing used in the rear has no definite set of symptoms that would indicate failure. A loose wheel could indicate a failed bearing. On one car, I had a knocking sound that was corrected with a bearing replacement. Another car just made a whining sound. On the 928 I replaced the rear wheel bearings after I had the car jacked up, brakes removed, and spun the hub. It sounded like it was filled with sand. Replaced the bearings and managed to cure some annoying vibrations at the same time.

Some will argue that that style of bearing rarely fails and I disagree. Especially when you consider that many are 20 years (give or take 5) old at this point and not driven regularly.

Someone posted something about rear ball joints. Don't try to look for them as they don't have ball joints in the rear. Loose brakes would be more likely to rattle rather then whine. But I guess it's worth checking them as well.

If you have a decent impact gun and a good air compressor, removing the axle nut and the upper bolt on the hub carrier isn't too hard.

 

And get that 140 wt out of there! Thicker fluids build more pressure, you are looking for seal falure at the very least by leaving it in.IMHO

 

The fact is ten years ago or so we rarely sold a rear wheel bearing now we sell quite a few. The dual angular contact rear wheel bearing is quite large much more robust the 911 style front roller bearings. In addition , the rears do NOT require setting the preload you simply torque to the spec of 460 NM about 350 lbs and it holds the two inner bearing halfs together. There is no adjustment needed.

 

I have a similatr grumble from the rear that started with the last set of rear tires. Sounded enough like wheel bearings that I was concerned. Put the original wheels with 10yo tires back on and the noise is gone. Recommend that you borrow a set of known-good wheels and tires to try before you go and spend a lot of $$ on bearings, torque tube, diff oil change, etc. Trying different wheels/tires is generally a no-cost test if you can coax a nearby owner to let you test with his/her stuff.