I moved the amp ground to the factory audio ground. Didn't fix issue.
When I unplug the rca's from the amp, the noise completely stops. Does this mean the head unit isn't grounded properly???
I attempted to ground the rca's from the head unit, but noise got worse.
RCA's do run along the passenger side, which is where the main power line goes for all the accesories for the m3. Hoping this isn't the problem.