10speed

I downshifted from 6th to 5th at about 2500 rpm on freeway and it started making a constant low vibration and sound like there's a small exhaust leak when the clutch is engaged at all speeds. I can feel a slight new vibration through the shift **** that disappears when the clutch is disengaged. The car has 113,000 miles, newer clutch. Any ideas?

Metronet

My 6 speed 3.0 had this humming noise around 1500 rpm in all gears. It's most noticeable when down shifting in a cold weather and rpm dropping from 2000 to 1500.

It turns out to be the power steering pump sucking air in. I did't expect it to cause such a huge vibration either but perhaps with 6 speed it's so smooth you could pretty much feel everything happening in the engine bay

Have a read, it maybe your issue, maybe not:

DIY: B6 A4 3.0 - Power Steering Noise Fix

10speed

Thanks for that! DId yours happen instantly though like mine did?

10speed

I took a look at the steering fluid level, it was low, I filled it a couple months ago also, luckily i have a container of the Audi fluid. I did not see any leaks around the hose where the link you gave me stated. I took it for a ride and the vibration seems gone. Where is all this fluid going, can
't be evaporating? Awesome advice, Thanks!

Metronet

I know my PS hard line has a very slow leak right between the firewall area.
It is visible only through the wheel well near the driver side tie rod.

I just topped up the reservoir as per the attached TSB and called it a day