two things:-
1. Yes you do get audio feedback to the ear this is called sidetone and is important that we can hear ourselves when talking, but this is normal audio frequencies.
2. If it only occurs when PTT is active then it is possible (but I am suprised on modern sets) that a Heterodyne effect is occuring i.e. the resultant frequency is the difference between the two (or there intermediate counterparts) and that this is not being filtered out (by being in the audible spectrum). This is not normal in FM sets but with a poweful enough signal bypassing/resonating with the IF (intermediate) stages could cause a problem, early boat VHF had similar problems. The other side would be that is poor EMC immunity and you have a found a "sweetspot" in their circuits.