hi people

Got a problem with a 2004 a3 2.0 fsi wondered if anyone could help or may of heard of similar problems?
On start-up from cold the car is great but once its up to tempreture i could only describe it as sounding just like a diesel,theres a low extra knocking noise that sounds like it may be coming from the timing chain end of the engine
Now ive changed the oil and filter just to rule out issues there but still the same so ive taken off the cam cover to look for any obvious signs there and taken off the cover for the timing chain to look for any excessive wear etc and cant see anything really obvious but i can depress the cam chain fully down with my thumb anyone know if that is normal or does it sound maybe a little weak??
Any help would be most welcomed as im really stuck now and really could do without a trip to the main *******s at the mo!
Thanks guys