As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 705 CLEARED FOR TAKEOFF, A LOUD BANG WAS HEARD AT 1.4 EPR CHECK. TAXI CLEAR OF RUNWAY AND PERFORMED A SECOND CHECK ON THE DE-ICE PAD WITH SAME RESULTS. AIRCRAFT RETURNED TO RAMP AND UPON INSPECTION FOUND THE PRESSURE RELIEF VALVE ON PACK DISTRIBUTION DUCT LOOSE. ADJUSTED THE SAME, RAN ENGINES WITH NO TROUBLE FOUND AND PACKS OPERATED NORMAL IAW MM 21-21-0 AND 72-00. AIRCRAFT RETURNED TO SERVICE.