What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: SHORTLY AFTER TURNING OFF THE LEFT PACK FOR BLEED, THE TRIP NUMBER 1 ENGINE ROLLED BACK WITH ACCOMPANYING THUMPING AND CLUNKING SOUND. WITH ENGINE AT IDLE, ENGINE INDICATIONS WERE NORMAL. WHEN POWER IS ADDED, A CLUNKING SOUND WOULD RETURN. AIRCRAFT AIR INTERRUPTED, BACK TO AND LANDED SAFELY AT DFW. REMOVED AND REPLACED NUMBER 1 ENGINE (AALA202506236217). PER J/C 08L40072003. ADDITIONALLY, REMOVE AND REPLACED THE ENGINE NUMBER 1 BLEED AIR REGULATOR (AALA202506240445). PER AMM 36-11-03. OPERATIONAL AND LEAK CHECK GOOD.