After putting on the aero kit, I decided to have my PDC sensors removed because I (1) hated using the PDC and (2) didn't want to drill holes into my aero bumper.

Now when I go into reverse, I have a completely different and higher pitched noise coming from the PDC, probably to warn me that there are no longer any sensors.

Where can I find either the power source or the speaker itself so I can rip it out of my mini and burn it in a bonfire?

 

There's probably just a fuse for it in the engine bay on down in the fuse box behind the cover by your left foot when sitting on the driver's side.

 

It's in the right rear quarter panel. Just pop the right rear cover off in the trunk, and both the control unit and speaker are mounted on a bracket inside the wheel well. It may be difficult to access if you have the H/K system since the amplifier blocks access. Just disconnect the connectors from the control unit.