What was found
WHILE TRYING TO TUNE HF 1 TO NEW FREQUENCY, THERE WAS AN EXTENDED (APPROX 10-15 SECONDS) TONE AND WHEN IT STOPPED WERE UNABLE TO TRANSMIT ON HF 1. ATTEMPTED TO TRANSMIT ON VHF 1 OR 2 BUT WAS UNABLE. SELECTED ALTERNATE ON ACP NR 1 AND COULD COMMUNICATE ON VHF 1 WENT BACK TO NORMAL AND WAS ABLE TO TRANSMIT ON HF 2 BUT EVEN THAT SEEMED WEAK. ACFT GROUNDED. REMOVED AND REPLACED THE NR 1 HF TRANSCEIVER IAW AMM 23-11-21, SYSTEM OP CHECKED GOOD. GROUND VERIFICATION GOOD.