i own a 1999 318i with M43 8 valve chain drive engine with 101,000 miles on, at 3000 rpm there is a definite rattle, from idle to2,500 rpm the engine is smooth and quiet, i have changed all the hydraulic lifters and rocker arms, also fitted a new oil spray bar, plus new timing chain and tensioners, but no change. i have been told it's piston slap or big end bearings but i'm not convinced as its had full bmw service history .