As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURNBACK / DECLARED EMERGENCY / ENGINE SHUTDOWN. LOUD "POPPING" NOISES FROM NR 1 ENGINE DURING ROTATION. ENGINE INDICATIONS NORMAL. PUSHED THRUST LEVERS UP & NOISES CEASED FOR 6-7 SECONDS. THEN RESUMED. INDICATIONS STILL NORMAL. DECLARED EMERGENCY, TURNED DOWN WING, THEN N1 (NR 1 ENG) ROLLED BACK TO 50 PERCENT. SHUT DOWN NR 1. FOUND SEVERAL 9TH STAGE COMPRESSOR BLADES MISSING MATERIAL. REMOVED AND REPLACED NR 1 ENGINE PER MT.