Loud squeal on Push to Talk

[BalsaBat]

I have a dual screen HDX system with SV-intercom-2S, but my nav/comm is from a Garmin GTN-650-xi. This is an existing installation (from about 2020), but has recently begun giving an overpowering squeal when I hit the passenger side push-to-talk button,. The squeal starts immediately and is clean like a tone generator was switched in, maybe at 600 Hz or so. It is also transmitted. Today it started doing it on the pilot side as well, but is more "scratchy". If I turn off the intercom power, the radio works fine with the fail safe (except I don't get the Dynon lady warning me about all the stuff she always likes to complain about). I saw a couple old strings here-in with a similar issue, but I don't think they mentioned that their system worked normally with intercom power off, or that it seemed primarily (or only) on one side of PTT. Getting to the antenna connection on the back of the GTN-650 will be a chore if its likely that. FWIW, I have a composite airplane with eight radial 3 foot wires for a ground plane.

Any thoughts?

Thanks
Ted

 

[GKC Aviation]

Because the squeal is being transmitted, and you can hear it in your sidetone, it is obviously on your mic audio line.
This won't be anything anything to do with antenna connections.
Personally, I would check the shield grounds of the shielded wires, especially the mic hi and lo wires.
I would also check the intercom unit ground itself. It might be as simple as a terminal has come loose.
There have been a few threads over the years here, and other forums where intercom or com squeal has been rectified with checking and repairing grounds.
The main ground wire comes out of pin 1 of the intercom connector. It is usually grounded at the same place as the VHF is grounded.
If this wire from pin 1 is not a solid ground, the intercom can attempt to get a ground through anywhere it can, including mic and phone shields (as they are all connected to this wire).
All the shield grounds are connected to this wire usually inside the backshell of the connector.
I have seen people do this shield jumper connection badly, and the shield wires start pulling out of the splices.
Might be a place to start anyway.
Come back to us with what you find.

 

[BalsaBat]

Thanks for that. I'll inspect/redo those grounds first. I did see that in general the shield connections were in the right overall configuration per the manual (though not "as close as possible" to the connector), but I've found some bad crimps elsewhere. Hope it's there.
.