I've got a DC 10-13.4 headset that produces unintelligible transmissions.
In which case there are two possibilities, the system its plugged into may be at fault so try connecting it to another system to verify the problem. If it is the Mic insert, it can be removed by undoing one screw, buy and fit a new one (Adams Aviation sell them), I had a faulty one and replaced it in 2 minutes.