Humming coming from the rear at all speeds. Fluids question too...

[audiquattrot]

Have had a slight hum barely noticeable hum for months. Recently it has gotten a bit louder, but not wheel bearing loud like I've experienced in past cars. The noise doesn't change pitch turning the wheel at speeds, which was normally the case when my old Audi had bad rear wheel bearings.

Could it be he differential? I always thought that a bad rear diff would only make noise when you accelerate. This makes noise even off the throttle.

I'm going to change the fluid this week front/rear.

75w90 for the diffs the choice you guys use? I could've sworn I used ATF on the front diff last time I changed it....but honestly I can't remember for sure

Also while I'm in there, I'll be changing the tranny (manual) fluid....MTL 70w80 ok?

[e30jps]

Front differential:
Spec: 90W GL-5
capacity: 0.75 qt
drain/fill plugs: internal (Allen) head, Size ?
commonly used after market oil: Redline Synthetic 75W90

Rear differential:
Spec: 90W GL-5
capacity: 1.8 qt
drain/fill plugs: internal (Allen) head, Size ?
commonly used after market oil: Redline Synthetic 75W90

Manual Transmission:
Spec: 80W GL-4
capacity: 1.4 qt
drain/fill plugs: internal (Allen) head, Size 17MM
commonly used after market oil: Redline Synthetic MTL (manual transmission lubricant)

Transfer case:
Spec: ATF
capacity: 0.6 qt
drain/fill plugs: internal (Allen) head, Size 17MM
commonly used after market oil: Redline Synthetic ATF

[audiquattrot]

Thanks for the list.....other sources I've read said to use ATF on the diffs which made no sense to me.....I think worldpac recommended that. Weird

[e30jps]

No problem man!

Maybe try and use this to find the noise its help me.... Auto Mechanic's Engine Sonarscope Hearing Device Tool Pinpoint Engine Noise Flex

Just put the car on jack stands and run the car and maybe can hear the noise with this tool.

[Sean]

I think I might have the same thing, except it sounds like ti comes from all sides of the car.

[audiquattrot]

its my rear drivers wheel bearing. Getting it taken care of today.

btw what a HUGE difference replacing the diff fluids. I was getting a pretty nasty vibration up front for over a yr. Couldn't diagnose it for a while, and gave up. Changing the fluid made all the difference.

[Sean]

Hmm, really? Good to know. I think the PO did the diff's fluids, but better check.

[Sean]

How many miles are you at?

I will say...it does sound like something a wheel bearing would do...

[audiquattrot]

How many miles are you at?

I will say...it does sound like something a wheel bearing would do...

I'm at 130k....had the wheel bearing changed and problem solved!