What was found
AIRFRAME NOISE & VIBRATION HEARD/FELT IN FLIGHT DECK & FA REPORTED IT WAS FELT IN THE FWD GALLEY BETWEEN THE L1/R1 DOORS. ONLY FELT IN CRUISE @ FL 340 FOR APPROX 5 MIN. ENG VIBS GREEN. REMOVED FROM SERVICE. PERFORMED FIM 05-50-00-810-801-A. DURING GVI OF RECIRCULATION DUCTS, FOUND GASPER DUCT DISCONNECTED. R&R TIC DOWN STRAP REF E175 AMM 21-24-03-400-801-A. NO FURTHER DEFECTS, AIRCRAFT IS OK FOR CONTINUED SERVICE. RETURNED TO SERVICE.