I'm helping out a friend on Thursday diagnosing a noise from his e46 M3.
The car is an SMG coupe.
He called me the other day; saying his car was making a 'rattling' noise from the engine bay.
It doesn't do it on idle at any particular revs (- or at least it's not noticeable.)
It's most noticeable from inside the car during acceleration.
Doesn't sound like 'marbles in a tin' vanos.
I'll be running a compression test first & will likely change the plugs for new NGK's at the same time.
Any suggestions for what else to check?