I have had exactly (and I mean exactly!) the same thing with my DC 13.4s. However, I immediately switched to COMM2 where, unlike you, the noise didn't happen and back to COMM1 where it did. So it definately was not the headsets in my case. The problem went away after an hour. That was 26 flying hrs ago an not a problem since.
At the time I just ignored it as London Inf were obviously not have a problem hearing with a radio check of readability 5.
The radio is a KX175.