01 Ford Mustang GT - This sound started coming out of the speakers when in the start position. It also cuts in and out when the radio is played.

I have no idea, maybe check the wires on the back of the radio, and on the speakers. Perhaps getting a short. Or a demon

Sounds like electrical interference with the wires going to the speakers. Not really sure what's causing it aside from it being an exposed wire somewhere but since the car isn't running I'm going to assume it's the wires going to the fuel pump.