As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
HF#1 RADIO TRANSMISSIONS UNREADABLE BY ATC IN FLIGHT. HF #2 TRANSMISSIONS ARE READABLE 5 BY 5 ON SAME FREQUENCY. GROUNDED - YES. CW B737-800 FIM 23-11 TASK 806. NO DEFECT ON GROUND AT ALL COCKPIT STATIONS. 5 BY 5 SIGNAL RECEIVED FROM OTHER STATION. GROUND VERIFICATION PASSED.