What was found
DURING LT ENGINE STARTING, STRONG NOISE WAS HEARD. CAPTAIN SHUTOFF ENGINE AND RETURNED TO PLATFORM. DURING CHECK, WAS DETECTED THAT THE NOISE WAS PRODUCED BY THE GPWS. IT WAS DEFERRED IAW MEL 34-29. DURING TRANSIT CHECK AT MEX, GPWS COMPUTER WAS REPLACED IAW MM 34-45-01. DURING OVERNIGHT SERVICE, GPWS WAS TESTED IAW MM 34-45-01, ALL CORRECT.