Originally Posted by
pipertommy
Which switch is that ? Sorry
I only know about the C172's that I fly, but I assume that there are similar arrangements on other GA aircraft...
There are at least 4 sources of sound - 2 VHF comms radio, a VOR and an ADF. You can select which of these delivers audio output to the headset with a group of selector switches. At one time I thought I would be clever and set-up a dual watch by tuning radio 2 to 121.5 while using radio 1 as my main comms and selecting 'both' as audio sources. As soon as I transmitted anything I realized that this was dumb because I heard my own distorted voice sounding distant and echoey coming back at me when I transmitted on radio 1. Obviously radio 2 was picking-up my transmissions from radio 1. I fixed this by selecting just radio 1. That sounds a lot like the symptoms you are experiencing and it could be the same cause.