Hey Ed,
Good to hear you are closer to the solution than I originally thought. Personaly I like to put all nav/communication electronics units on a separate power/ground circuit. (keep them isolated from ignition/pump moters, etcetera) The exception to this maybe the radar dome/array motor feed.
I like the comment someone else made regarding the mike being a likely culprit;could well be. I'm not sure, but the more I think about it, it could be loose/shakely connections in the mike. Intermitent problems are the absolute worst to troubleshoot. Good luck.
If you'd like, email me at
customercentric@verizon.net and we can set up a phone call. I'm not far from you. I know a couple of pretty good marine electronics guys.
P.S. I've an older S/H VHF I don't use that you could borrow or buy for short money, if you'd like/need.