I am the proud owner of a new (used) 2002 Audi A6 3.0 automatic. It was a salvage purchase from a friend who's buys at insurance auctions and when he got it the front end was smashed up because of a collision but he's good at rebuilding and so I now Its very nice! But there is a slight rattling or raspy sound when I accelerate and I'm concerned that whatever is wrong might cause more problems if I don't fix it so can someone please help me with this?