DURING APCH TO LNDG PLT HAS NMAC.

Narrative

WAS APCHING FROM THE SSE. CTL TWR HRS WERE CLOSED; IT WAS NO LONGER CLASS D. I WAS USED TO THE TWRED APCH FROM THE SSE. RWY 33 WAS IN USE; AND THE TWR ALWAYS BROUGHT TFC STRAIGHT IN. I WAS MONITORING CTAF; MADE POS CALLS. ALL SEEMED TO BE QUIET AND LOOKED TO BE AN UNEVENTFUL APCH/LNDG. WAS MAKING CALLS; STATING STRAIGHT IN; 'TFC-PERMITTING;' AND THEN; ABOUT 2 MI OUT; BEGAN TO HEAR CALLS OF ACFT IN OR ENTERING THE PATTERN. ABOUT 1 MI OUT; HEARD A SENECA CALL ON THE DOWNWIND. I CONTINUED TO MAKE CALLS. THE SENECA NEVER ACKNOWLEDGED MY CALLS. I KNEW HE MUST BE CLOSE; AS HE WAS FASTER. HE CALLED BASE ABOUT THE TIME I WAS ABOUT ONE 1/2 MI OUT AND STABILIZING FOR THE DSCNT. SECONDS LATER; I SPOTTED HIM (FIRST TIME); DESCENDING; APCHING FROM MY 2 O'CLOCK POS. I SUSPECTED HE COULDN'T SEE ME (OR ELSE WAS IGNORING ME). I HESITATED FOR A SECOND; AND THEN MADE A RATHER ABRUPT 90+ DEG DESCENDING R TURN; GOING BELOW HIM. AT THIS POINT I WAS LOW; OVER A NOISE SENSITIVE AREA. I WANTED TO CLEAR OUT OF ANY OTHER BASE TFC. MADE RADIO CALLS STATING I WAS LEAVING THE PATTERN.