As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT, HF #2 RADIO STARTED INT TRANSMIT ON ITS OWN. WED HEAR THE TUNING TONE AS WELL AS SFO RADIO'S TRANSMITS HOWEVER WE COULDN'T TRANSMIT OUT WITH EITHER PTT SWITCH. GROUNDED - YES. ACCOMPLISHED HF COMMUNICATION TEST COM B737-900 FIM 23-11 TASK 806 ALL OPS CHECK OK DEFECT CLEARED. ACCOMPLISHED TASK 23-11 TASK 801. HF BITE PROCEDURE OPS CHECK OK.