Just asking;
Have you tried taking the PTT out of the loop and using just the radio and headset? Just key the mike with the radio PTT. Some PTT are wired funny (DC comes to mind). Also; are you using an intercom? If so unhook it.
You seem to have a feedback loop going on.
Start with just the radio (working or not?). Add the headset. Add the intercom. Add the PTT.
At some point you will go from useable to crap. Crap portion can always be fixed.
Hope this helps
Chris