thanks for all advice. I had previously tried using music ear-plugs and could not make them work at all. But I realise now I messed up the adapter I made to convert the tiny plugs they use to aircraft plugs. The tiny plugs are stereo, and I confused the connections to the mono aircraft plug. With the adaptor fixed, all my collection of music earphones now work with my radio. Some greatly accentuate the 'hiss' but some sound good. I'll try a few, then ditch the David Clark headset (I have a gooseneck mike).