[Biturbos4] S4 Avant - turbo problem?

[Robin Gibson]

Hi

Over the last 1000 miles I have noticed some unusual engine noises;  at low revs on light throttle, there is a low-pitched whistle or drone which sounds like one of the turbos getting up to speed slowly.  On more throttle or once the turbos are spinning, the noise is not apparent.  At higher revs (above 5000), there is a high-pitched buzz/chattering sound.  Neither noise would mean much to anyone who doesn't drive an S4 regularly.

The engine is slightly slow to pick up at low revs, but feels generally ok above 2000rpm or on heavy load.  I replaced the turbos about 20,000 miles ago after the manifold developed hairline cracks, but the noises this time sound quite different.  I suspect maybe a wastegate problem or perhaps an air leak somewhere

Has anyone experienced this before?  I have read many emails discussing boost gauges and the VAG COM; would a turbo or hose problem show up with either of these, and is it easy enough to rig up something temporary to check?  

I'd greatly appreciate any advice anyone can offer, as I have mentioned it to my dealer but he doesn't want to know until something blows up.  Might suit him, but I don't fancy waiting... 

Ta

Robin Gibson
1999 S4 Avant abt 310

e-mail: robingibson at cowanlinn.co.uk