I've seen another post with this title but no solution so I thought I'd post similar to see if I get responses.

Basically, decelerating/acceleration but more pronounced when slowing down I hear something that sounds like a buzzing / rattle / tin can vibration sound that I can't track down. It's really cheap and annoying sounding, but for the life of me can't pinpoint if it's just a loose heat shield under the car or something else. It happens just below 2000 RPM (maybe around 1800 is the peak of the noise), and is louder after the car warms up. When I put in the clutch and the revs drop it goes away. Strangely it doesn't occur revving the car in neutral while stationary. Something harmonic is occurring with the clutch engaged that causes the noise to happen. Driving in the city it's always present as I slow down for stop signs and lights, or cruising around a slow zone.

Has anyone experienced something similar and found a fix? I doubt it's serious, it's just not a rattle I can live with (unlike most of the interior ones which don't bother me.) Makes the car sound like some ghetto hooptie or broken old pickup truck judging by the tone and timbre of it. Ideas?

 

Update:

Took it to the dealer, after engine had warmed up on our drive, the service adviser and tech both agreed there's a noise present, but weren't sure if it was normal or not.

We discussed the TSB on N18 wastegates, which for most people is a condition that goes away when the engine is warm. This gets louder as the engine is warm, but seems to be boost related: you can modulate the sound in gear by how much throttle you're giving it. They offered a new turbo assembly for free come fall, suggested drive it for the summer and see if it gets more pronounced.

Any other JCW/GP2 and N18 S owners noting a rattle between 1800-2k RPM? It doesn't seem terminal, it's certainly no timing chain rattle. Seems to be a fairly rare thing though.

 

Mine just started doing the same rattle. I don't drive my mini daily. I usually take the motorcycle (perk of san diego). I hope you get an answer as to the issue.