Much of this information is from www.audiworld.com. there have been numerous turbo failures on the earlier 2000 Audi S4. For the people that have had turbo failures, some have indicated an abnormal 'siren' sound when accelerating. There have been a few turbos that have also been replaced (without failure) because of complains of this sound. My car started exhibiting this sound from 2K miles onward. Initially, this sound occured only when the engine was cold. It is however now more apparent most of the time. I have brought this to the attention of the Audi service department but have insisted that sound is normal and is apparent even on new cars. Since then I have test driven a new S4 and the sound is not present. The theory to the current failure is that there is an insufficient oil supply to the turbos and because of this the internal bearings are damaged and hence start whining ('siren sound')and eventually failing. A few changes by Audi also supports this theory. 1) they have revised the turbos on the newer S4S. The oil inlet to the new turbos are now larger. Also,2) they have revised the recommended oil weight from a 5-40W to 0-30W which ensures better oil flow and lubrication at lower temperatures. The reason of my concern is that the turbos cost more than $5000 dollars to replace and I intend to keep my car for 5 years or 90K miles (whichever comes first). Fyi the 'siren' sound is sometimes loud enough that passengers in my car think that there is a emergency vehicle in the vicinity. I would be more than happy to assist you in any way, or provide you with contacts, literature on individuals that have experienced turbo failures.

- Keller, TX, USA