I've read in the forums about cold start engine knock coming from passenger side of engine. Goes away after warmed up. My car has done this since day one. Finally took car to dealer with 3,000 miles on it to document the knock and fix some other stuff. Problem was diagnosed as no o-ring gasket found between header and exhaust pipe flange. Installed gasket and to my relief no more knock. I wonder if any other 01's left the factory without this gasket??? My build # is 3597.