I recently purchased a 2008 A4 2.0T (not a quarto) with 76K. It seems to have an unusual engine sound when accelerating in neutral or while accelerating when driving. Seems to be most noticeable when cold. I had a pre purchase inspection by an independent dealer and then had a local Audi dealer do a transmission service. I mentioned this sound and according to the tech it was normal and thought it might be the secondary air induction. Any opinions on this and if anything can be done even including some type of insulation maybe under the front carpets or engine compartment. If this is a normal sound at least I won't her the noise as it is annoying.

 

No Audi I've ever driven that was in good health had any unusual noises. It shouldn't be the SAP system unless you're driving immediately after starting from cold, as the air pump shuts down after 30-60 seconds and only functions when the engine is cold-started. Start by checking and verifying all fluid levels and condition (coolant, oil, transmission, power steering), and replace or top off any that need it. That's a solid first step.

 

when you say a sound in the engine? Do you mean a type of knocking? is it smoking at all?