Could just be the coil packs giving you a faint ticking which is normal. I heard they are notorious for giving up on 4.2s which would give you misfire CELs. Audi has revised them for up to Revision Q. Has the performance decreased?
I am looking at a touareg with a 4.2 in it but it has a tick the dealer has replaced the tensoiner and other stuff and it is still ticking it sounds like a lifter/lifters to me how hard are those to relplace or what do you think this is. this truck is going dirt cheap he has givin up on it so im trying to take advantage here. thanks