[st86good]

I have '11 328i with N51, 60k mi.
My engine mount replaced recently with transmission fluid and filter.
(6L45)
I didn't noticed til now but when I was parking in parking garage today, it made rattling sound for like 0.5 sec every time i am stationary and pushing gas pedal to move.

it just goes away in 0.5 sec, so i can't find reason.

I already replaced belt and belt tensioner so I am unsure that makes noise.

here's video. it sounds like diesel engine for half a sec.

Any input will be appreciated.

https://youtube.com/shorts/003JEuUlDXk?feature=share

[sabino56]

I had the alternator pulley (it has an overrunning clutch in it) go bad once and it made a strange rattle that was hard to track down. Hard to say if same as yours but easy to check. It should be free to turn w/o turning alternator in one direction. Google for info.
Also, remove the belt and see if sound goes away, if so likely one of the components on the belt. You can find shorter belts to bypass a/c or power steering if needed to narrow down.
Good luck

[st86good]

Originally Posted by sabino56

I had the alternator pulley (it has an overrunning clutch in it) go bad once and it made a strange rattle that was hard to track down. Hard to say if same as yours but easy to check. It should be free to turn w/o turning alternator in one direction. Google for info.
Also, remove the belt and see if sound goes away, if so likely one of the components on the belt. You can find shorter belts to bypass a/c or power steering if needed to narrow down.
Good luck

Thank you. It was loosen engine mount. Somehow shop just hand-tightened them. BMW dealership found out, tightened to spec for free. Generous place