Noise in speakers when rear defrost on?

I have a Pioneer DH2700 in my 96 Formula with power ant. When I kicked on the rear window defroster I get a LOT of static thru the radio.
Suggestions?

If everything else is stock as in no amps etc, its prly a poor ground behind the radio or poor antenna ground

It's also possible that defrosting traces on glass or wires to them/relay are damaged and arcing, as it's pretty good current going through.