Ok, so I understand this, when you are not transmitting you are hearing feedback?
Feedback is caused by the microphone not being muted and it picking up the sound it is transmitting. Or it is caused by transmitting while sounds are being played.
In either case, the mic must be keyed in order to get feedback. If we are indeed talking about true feedback.
Now, if you are gearing feedback sound from a VOX transmission when your mic is not keyed, then I would suggest the person who is transmitting does not have thier mic muted and they are transmitting feedback sounds.