Hello, I am new to this forum but am very much liking what I have read so far.
Well, I have a 2001 Audi A6 2.7T with around 110,000 miles that has begun to make this loud noise when I start her up. It is sort of a whirring/revving sound but the RPMs stay normal. The whirring-like sound is followed by a higher pitched moan that fluctuates on and off. It sounds slightly like a belt, but nowhere near as high pitched as a slipping belt whine. The sound gets worse when I turn the steering wheel.
However, after driving it for a little while, the sound goes away. If I turn her off after driving a bit and then turn it back on, the sound does not come back. The sound only occurs if the car has not been driven for a few hours.
Any suggestions?
Thanks!

-Sam

 

See if you can locate an approximate where the sound is coming from. My initial thought is the SAI pump. Center rear, top of the engine compartment just behind the y-pipe.

 

Or a failing belt tensioner on the serpentine belt (bad but not deadly) or the timing belt (deadly).

 

If... it Only happens when it's cold.
If... it Doesn't happen after it's warmed up or when it's warm out.

Then the Power steering pump is cavitating (sucking in air and whining)

If that is what it turns out to be you will need to;

Replace the fluid with the improvedG4000 from Audi dealer 3-5 qts I can't remember.

Replace all those ridiculously un-engineered Chinese ear clamps with non-perforated hose clamps. Search them on-line (i can post a pic if needed)

Replace the crush washers on both sides of the banjo bolts that secure the power steering hoses to the pump.

Note: The pump will tend suck in air rather than leak it out.
so a loose hose, clamp, or seal... may not leak when car is off but will allow air in while it is running.

To check:
Simply start the car cold while it whines open the cap to the Power steering reservoir and it should not be foamy or creamy. It should be dark oil/fluid. If it is foamy, that is due to air bubbles trapped inside the oil. The air does not compress like the fluid so the pump vibrates creating all sorts of whining moaning noises.It is most likely to do it in the cold.

This sounds like your problem. So get it taken care of soon or you'll mess up your pump. In the mean time start it and let it warm up 5-10 minutes or so before cutting the wheel, the warmer the better. Avoid cutting the wheel with cold fluid you will make more air bubbles that way.