What was found
EXPERIENCED LOST COMMS ON APPROACH. HAD A CONTINUOUS CLICKING NOISE THAT INTERFERED WITH ATC AND A CONTINUOUS TRANSMIT "TX" ON THE NUMBER 1 RADIO. HAD NO COMM AT ALL AT LANDING. TURNED BOTH ARCDUS OFF AT ONE POINT AND STILL HAD THE CLICKING NOISE. POWERED DOWN PLANE PER ATC REQUEST DUE TO INTERFERENCE. REMOVED FROM SERVICE. REPLACED NR 1 ARCDU IAW AMM T/C 6238101. PERFORMED LLM RTS TEST IAW MTC 6238101 AIRCRAFT REMAINS CAT 111 QUALIFIED COCKPIT PLACARD REMAINS CAT 3. RETURNED TO SERVICE.