first thing to do is re-check the connections on the mic plug inside the radio.
if you soldered anything to the TX pin, there is a chance that when you took the RB board out, you moved the wire on it to where its barely connected.
when you key the mic, it ungrounds the receive wire so the speaker cuts out, but you may not actually be TXing.
also make sure its not just the S meter acting up by verifying the same intermittent output on a wattmeter.
LC
if you soldered anything to the TX pin, there is a chance that when you took the RB board out, you moved the wire on it to where its barely connected.
when you key the mic, it ungrounds the receive wire so the speaker cuts out, but you may not actually be TXing.
also make sure its not just the S meter acting up by verifying the same intermittent output on a wattmeter.
LC