As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A STRONG ELECTRICAL SMOKE SMELL AND LOUD SQUEAL FROM THE CABIN ADDRESS SPEAKERS WAS CAUSED BY AN INTERNALLY SHORTED CABIN SPEAKER AMPLIFIER. THIS PROBLEM COULD NOT BE ISOLATED UNTIL THE 'CABIN AMP' BREAKER WAS PULLED. THE BREAKER DID NOT TRIP ON ITS OWN AND CONTINUED TO FEED THE SHORT.