OK, so I finally had time to open it up and have a look. Sorry for the delay. It turns out that the hissy, click audio was from the wires going from the AGC board to the volume pot. I have them connected using header pins. They had pulled loose and were almost falling off. When I pushed them back on firmly the problem went away? The mic click/pop is still there but reduced, so I think it's back to near normal.
73, Dan W2DLC?
