Nice clean install.

For the interference, bad ground is a common cause. Normally, interference normally goes with engine RPM so maybe it's not related to the ground. Since it's close to the radio, I wonder if that can be a cause. You could try removing the fuse for the radio to shut it down completely because when you turn them off, they are more in sleep mode than really off. There are components that remain powered.

I might be way off, but those are the first things that come to mind.