Hey there...I'm a newb on this forum but I'm hoping for some feedback regarding a high pitch whine (more of a howl) coming from my right rear (ish) drivetrain.

Some back ground real quick:
2000 S4 with 95k miles, Stage 3, drivetrain wise I have 034 snub mount and cage, 034 street density tranny mounts, and Apikol rear diff mount and carrier bushings. (motor mounts are still stock...call me lazy )

At first I figured it was the too common wheel bearing...but I replaced the right rear 11 months ago...and quick S turns to load/unload it do nothing to the pitch or volume. It is for the most part only audible from about 57 to about 80 mph or so. It doesn't matter what gear I'm in...I've downshifted from 6th to 5,4, and 3 and the pitch or volume doesn't change. The pitch goes up with speed and it gets louder the further I drive at highway speeds...almost like it heats up and really starts to hum if I drive over 15 mins on the freeway. The kicker is...it goes away when I let off the gas. Say I have the cruise on at 65 mph and I coast down a gradual hill...the sound is gone...but as soon as it levels out and the engine/drivetrain picks up a load again it comes back. And when you head up the next hill and the load increases it will really start to hum.

I serviced my rear diff...fluid was dark but no chunks or anything abnormal. No effect on the noise...its actually getting worse progressively as time goes on.

The last time my wheel bearing went bad a year ago...it made noise at all speeds even around town so this has me baffled. But let me tell you...this is LOUD after a half hour on the road...you can hear it above the stereo clear as day. The best way I can think of to relay the sound would be to imagine the sound you get from rubbing a wet finger in circles around the lip of an empty wine glass...but make it grainy like it was coming from the drivetrain of course

My next thought was maybe the right rear CV joint is going south...but there is no tear in the boot. Honestly I can't think of anything else to replace besides the diff itself...but it only makes this blasted humming at freeway speeds and the fluid change had no effect. I know that the apikol rear diff mount is going to amplify anything and everything and expected that...but it keeps getting worse and now my wife wont even ride in my car...puts the two year old to sleep though so not all bad lol.

Please...any input would be great. I hope I was thorough enough in my description. Take care and Happy New Year!

 

I forgot to mention I have the AWE DTS

 

fuel pump?

 

Would a fuel pump only make noise on at highway speeds and go up in pitch as I accelerate from 60 to 80 though? I read some posts on noisey failing fuel pumps too...but how could I verify/check that one?

 

I gave it a shot for good measure but I really dont think its a fuel pump issue. If that were the case I would hear it driving around town in third and fourth gear at approx 2500-3000 RPM. I tried it in the garage like you mentioned to be sure but heard nothing. Can anyone confirm or deny the possibility of a worn out CV joint in the right rear? Can they wear out even if the boot is intact and cause a hum at highway speeds? Has anyone had a diff go bad that could relay what they heard when it happend to them?

 

Jack up the rear and roll each wheel. See if the right side sound different than the left.

Also, look for any mounts that are broken. My CV's are wearing out in my driveshaft, but I don't have any high pitch whine coming from them.

 

I'll get it up on a lift tomorrow and report back. Thanks!

 

I got it up on a lift and checked mounts and rotated the wheels but everything seems solid and sounds the same. Has anyone had main driveshaft CV joints or the center support bearing between the tranny and rear diff fail on them? What could that sound like? Maybe the culprit? Thanks!

 

kinda sounds like a transmission front case bearing. It doesn't make the noise if you're coasting with your foot off the gas, but it does when you step on it?

 

I have a Mustang with the same symptoms, but I know that it is the ring and pinion in the Mustang. We had some new gears installed. They had always been noisy, but the longer we drive it , the more it sounds like what you describe.

I have heard of wheel bearings being installed wrong and going bad soon after install. If the bearing was pressed into the hub without a center support, the center can be pressed out.

Keep us updated.