I have the same problem, but with the internal microphone as well. But it happens not often. After a few seconds it stops transmitting. The other end hears a noise, somewhat like a roger beep. The LED turns to yellow /orange, i.e. both LEDs are on. And it is on receive.
I'm using the GD-77 with a DVMEGA simplex hotspot.
Latest firmware, 15/03/2020 [bc46565]
73s,
Jens