As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 3732 -ATB/IFSD- RETURNED TO BTV DUE TO LEFT ENGINE IFSD. FLIGHT CREW REPORTED ENGINE VIBES ON CLIMB OUT FOLLOWED BY POPPING AND ENGINE ROLLBACK TO IDLE. CREW SHUT ENGINE DOWN PER QRH. CORRECTIVE ACTION: FOUND EXCESSIVE PLAY IN THE HMU/FUEL PUMP ASSY. MAINTENANCE REPLACED NUMBER 1 ENGINE HMU/PUMP ASSY, FUEL PUMP QUAD RING, FUEL PUMP CARBON SEAL AND FUEL PUMP GEAR PACKAGE. REF B737 AMM 73-11, 72-60 AND 72-63.