This sounds an awful lot like the problem the NORCAL guys had when they released the 38 Special transceiver kit many years ago...They nicknamed the issue 'The Thump" .Not sure they ever came up with a solution..try to track down old issues of QRPp..there was a lot of discussion about it in there. There maybe some folks on QRP-L that were around during that era.
Brian K9WIS
