contacted bmw corporate, was getting an engine malfunction on above 115mph...dealer replaced left turbo for free, it failed their turbo test. oil consumption slowed down, mph went back up, no more knocking...must have been a gasket or seal on the boost side? no clue....just hit 80000 miles, they dropped a new trans in for free too, wasn't staying in 4th 5th or 6th. brand new now! cant keep it under 100 on the highway, so smooooooth