Check Antenna Couplings
I had a bad intermittent static problem with my radio reception and transmissions and discovered during some unrelated work that my connection to my antenna was faulty. Redid the connections and the problem disappeared. Good luck with your hunting.
Jim Harris, RV7A, 2nd owner, N523RM
IO-360, Hartzel CS prop, Older Aerotronics built panel Dual GRT Horizon WS, GRT EIS, Garmin 340, 335, Dual 430s, TruTrak 385 A/P with auto level, FlightBox hard wired to WS, Dynon D10A with internal battery (backup EFIS), 406 MHz ELT.
Retired - Living the dream - And going broke!