WHAT YOU HAVE IS RFI, RADIO FREQUENCY INTERFERENCE
BACK IN THE DAY, BEFORE 1980'S SPARK PLUG WIRES CAUSED THIS AUDIO PROBLEM... IT'S CAUSED BY HAVING A BARE POWER WIRE OR UNSHIELDED ELECTRICAL DEVICE THAT EMIT'S SPURIOUS RADIO WAVES
ANYTIME YOU HAVE A SPARK OF ANY KIND IN AN ELECTRICAL...