My 6 month old FT-991A just started generating serious feedback through the speaker when the microphone is keyed. The antenna is fine, less than 1.2 on 40M, where I was working. Coax is good. Ground is good. It will do it with the power down to 5W. I can't say exactly when it started. I've been mostly listening recently. The only thing I did different was trying to use the USB and RS-232 interfaces with Ham Radio Deluxe to receive data. Everything is now disconnected. Any advice would be appreciated.