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I have had my Humminbird Sonar GPS mounted over my marine radio for 2 years at least-no issues in the past. In the last week or two, when the unit is on I am getting feedback on the radio. Hard to hear when people are talking. If I reach down and shut off the Humminbird, the radio works fine, so I am thinking it has something to do with the GPS signal in some way. No change in wiring and no movement of the units, all in the same place for a long time.

You have a ground on one or the other going bad "maybe both". Most likely the radio though

I'm having the same issue. Humminbird unit is near my vhf antenna. Never had a problem until I changed over to a new Humminbird with GPS included. Checked radio and antenna with a meter & found antenna bad. Replaced antenna & radio (it was getting old) but it wasn't problem. Turn off the Humminbird and the interference goes away. Going to try moving the unit away from the antenna to see if it helps.

Wevans has it right. Bad grounds do these kind of things.

Dubble

Thanks. That makes sense. I have had ground issues on the boat over the years, so that is likely. I will play around with it and see what it does. I knew someone would have an idea. Thanks again.