What was found
(CAN) CREW REPORTED FLICKERING EADI & EHSI, ALTERNATING, ON BOTH THE CAPTAIN`S & CO-PILOT`S SIDE. IN CONJUNCTION WITH THIS A LOUD NOISE WAS ALSO EVIDENT OVER THE COCKPIT AND CABIN SPEAKERS AS WELL AS THE CREW HEADSETS. TROUBLESHOOTING WAS CARRIED OUT & THE NR 1 & NR 2 INVERTERS 26VAC TRANSFORMER GROUND TO LOWER RT JUNCTION BOX MOUNTING BOLT WAS FOUND LOOSE. MAINTENANCE RE-SECURED THE MOUNTING BOLT AND THE SYSTEM WAS FUNCTION CHECKED SERVICEABLE. ACFT WAS RETURNED TO SERVICE. REF WMD 129-340016, SHEET 4.