New owner here having recently acquired a 2011 e90 M3 6MT a few months ago. While I love the car, I've had a few issues (bad 02 sensor, plugs and air pump) and things have been running great for a few weeks until I just noticed a knocking sound.
It doesn't seem to be coming from engine but rather underneath and on the driver's side. I only seem to notice it at idle and it's irregular. Sounds like knocking on plastic or like when you have some change in a laundry dryer. If I restart the car it starts back up after a minute.
Luckily the car is CPO with original warranty so I'll be contacting the dealer but wondering if anyone could identify it.
Here is a crummy video. Couldn't here it until I moved my phone near the wheel well: