UNAUTH RWY ENTRY.

Narrative

WE HAD TAXIED FROM OUR RAMP TO INTXN M WHICH IS APPROX 100 YARDS. DURING THIS TIME WE WERE RUNNING CHKLISTS. MY FO HEARD WHAT HE THOUGHT WAS A CLRNC FOR US TO TAXI INTO POS AND HOLD. ALL I REALLY HEARD WAS HIS READBACK AND THOUGHT I HAD MISSED A CALL. I RELEASED THE BRAKE; TAXIED ACROSS THE LINE WHEN I HEARD THE CTLR TELL US THAT THE CLRNC WAS FOR A COMPANY ACFT AT THE END (FULL LENGTH). I APOLOGIZED; MADE A 180 DEG TURN AND LEFT THE INTXN. I NEVER ACTUALLY TAXIED ONTO THE RWY. NO TFC CONFLICT. WE ACKNOWLEDGED TO THE TWR 'POS AND HOLD.' PROB AREAS: COMPANY PROC TO MONITOR COMPANY FREQ WHICH LED TO 'TOO MUCH CHATTER IN THE COCKPIT.' AT SOME AREAS AT THE SEA ARPT THERE ARE 'HOLES' OF RECEPTION. WE HAVE TO HOLD THE SQUELCH BUTTON TO HEAR THEM. IF 2 AIRPLANES ACKNOWLEDGED A CLRNC; TWR SHOULD HAVE ENSURED WHO READ BACK. ALTHOUGH I HAD NOT AWARE OF MISSING A CLRNC I SHOULD HAVE HAD MY FO CONFIRM THE CLRNC SINCE I DID NOT HEAR IT. CORRECTIVE ACTIONS: I AM REDUCING 'RADIO LISTENING LOAD' DURING CHKLISTS AND ADJUSTING CRITICAL VOLUMES AS NECESSARY AND BEING EXTRA CAREFUL TO ENSURE WHAT CLRNCS I HAVE RECEIVED OR NOT RECEIVED. SEA TWR SHOULD LOOK INTO THE PROBS WITH RECEPTION OF THEIR XMITTER(S) AROUND THE ARPT ENVIRONMENT.