What was found
AFTER TAKE OFF A-F/A INFORMED US L-1 DOOR WAS MAKING EXCESSIVE AIR NOISE LEVELED OFF AT 15000 AND DECIDED TO RETURN TO DEP AIRPORT LOWER DOOR HINGE COVER NOT IN CORRECT POSITION. GROUNDED - YES. DIVERSION TIME 16 MINUTES - COMPLIED WITH ASA 800-52EA-20774, REFORMED DAMAGED LOWER DOOR HINGE COVER AND APPLIED SPEED TAPE ON TORN RUB STRIP. ACCOMPLISHED LEAK CK REF B737-800 AMM 05-51-91 NO DOOR SQUEAL NOTED AT AFFECTED AREA.