Rite not sure about this but just had timing belt and tensioners done on my S3, now when it's idling an I rev it an let the revs drop to normal I get what's sounds like a single pop coming back down the CAI? Abit like an echo down a drain pipe? Sorry for the **** explanation!! Any one had this or know what it could be, all the timing is set up correctly. My engine man light did come on after belt fitting, so scanned it an it came back with camshaft sensor. Cleared the fault drove car and it drives perfect boosts as should an no faults come back up?!