Radio - Side Tone Feedback

[Skates97]

During annual in December we cleaned up a bunch of old wiring behind the panel, apparently over the years when someone had removed or added things they just left old wires back there snipped off...

Ever since when I use the PTT on the LH yoke I get feedback (high pitch whine) but only when using my #2 radio (Garmin SL-40). With the #1 radio (Narco Mark 12D) there is no feedback. The PTT on the RH side generates some feedback on the #2 radio, but it is not as loud as when the LH PTT is used. I am assuming it is a ground or wire from the mic jack, maybe a wire that is running next to something it wasn't before we started cleaning things up? With it affecting only the #2 radio I was going to start with tracing either the ground or the wire from the mic jack to that radio (the next time I feel like crawling under the panel). I thought I had read in a post that you could get feedback if the PPT and radio were grounded at the same point, but that is a fuzzy memory at best.

[Skates97]

When something is different, start with what has been changed. Troubleshooting which works in the air, and on the ground.

As I said we cleaned up a bunch of old dead end wires behind the panel during annual. We also replaced the old antenna cables with RG-400. Trouble shooting a little more and found that the whine was audible coming from the radio when the PTT was pressed, you didn't have to have a headset on to hear it. This also was occurring without the engine running so it was not coming from the generator or mags. I started with the coax cables, clipped the zip ties holding everything together, separated them, whine is gone. Re-routed the cables and secured them, whine still gone. For whatever reason the way they were run was causing the issue. Glad to go fly without that annoying sound.