Zipping noise coming from Engine compartment below 2000rpm

[randle]

Hi

I have a strange zipping noise coming from the engine case area when idle and accelerating which goes when the revs pass 2000rpm. I've had a capable mechanic have a thorough look at this which includes taking the engine casing off to see if anything is knocking or rubbing against the case but there hasn't been anything obvious at all.

This isn't the turbo sound as it's not a whistle and if that was the case you'd expect it to get worse when it's working harder not just dissappear so i'm really stumped.

The mechanic has even spoken to a couple of Audi dealers who couldn't really help so am worried that this is going to be an expensive discovery

We've had a VAG reading on the car but this doesn't flag anything!!

Any ideas?