What was found
UPON NOSE GEAR RETRACTION, LOUD THUD. GRINDING NOISE ENSUED AND GOT LOUDER. DECLARED EMERGENCY. NO UNUSUAL INDICATIONS. (FLT 3532) CLOSED REMOVED AND REPLACED THE LOWER PRESSURE TRANSDUCER FOR HYDRAULIC SYSTEM NR 2 IAW AMM. OPS CHECK GOOD, NO DEFECTS NOTED. ALSO PERFORMED SYSTEM NR 1, 2 AND 3 HYDRAULIC SYSTEM BLEEDS. SERVICED HYDRAULIC SYSTEMS NR 1, 2 AND 3 IAW AMM. NO DEFECTS NOTED, A/C OK FOR SERVICE.