What was found
AIRCRAFT WAS GROUNDED: - DECISION WAS MADE TO RETURN TO ORD - EMERGENCY DECLARED; ACFT LANDED OVERWEIGHT WITHOUT INCIDENT - DURING CLIMB AT APPROXIMATELY 8000' AFL, A VERY LOUD SQUEAL WAS EMANATING FROM FWD SERVICE DOOR. NO DOOR ANNUNCIATOR LIGHTS ILLUMINATED. CONTINUED CLIMB TO CRUISE AT FL360 & WHILE NOISE HAD DISSIPATED SOMEWHAT, IT WAS STILL VERY PRESENT. AT CRUISE CABIN ALTITUDE INDICATED APPROX 7000' AND 8.0 PSID. DURING DESCENT, SQUEAL SILENCED DESCENDING THROUGH APPROX 16000' AFL WITH 4000' CABIN ALTITUDE AND 4.0 PSID. CLEANED AND INSTALLED FILLER TO AFT LOWER SEAL DEPRESSOR. SANDED PRIMED AND PAINTED. PRESSURIZED AIRCRAFT TO 8.0 PSI NO SQUEALS OR NOISE NOTED PER AARD 51-00-00-2.