Ground loop or something else?

Hi Folks, I have a siren-like whine that occurs WITHOUT the engine running. The whine only shows up on AM radio. All other sources are pefect. Yanking the antenna plug gets rid of it, but all radio reception with it. Car is a 2006 Subaru STi with an in-glass rear antenna. System is Pioneer AVIC Z1 and an older XTant AMP on a rack attached to the back seat. I have tried a ton of stuff from notes in this forum including: Single ground source for amp and headunit Running new RCAs over the seat to get away from any induced noise. PUlling the RCA from the headunit does NOT help. Whine still appears in rear speakers powered by headunit. The only connection to the headunit at that point was the remote turn on. Yanking that kills the whine as well. Is it possible the older amp is creative some induced noise in the rear window antenna? Starngley enough the whine leaves one AM channel and moves to another that was previously unaffected as the amp warms up. Should I try a ground siolator for the antenna? Any other ideas? Thanks, folks. cgardnerma

I would say if it is only on the AM channel then it's nothing to worry about...people still listen to AM?1968 VW Beetle

Pioneed DEH-780MP, 2 10' Memphis PR104D, Memphis PR500.1, TXC 6.1, MTX Thunder 8502

I'm not worried, I just wanted to know if folks had any ideas, because I don't like listening to the siren-like whine. As for AM--as long as the Red Sox are only on AM in Boston, I am stuck with it.

try grounding the antenna shieldProve your connections, use a meter!

I promise, I'll behave!