What was found
SHORTLY AFTER TAKEOFF & PASSING THROUGH 10,000' AGL, THE CREW EXPERIENCED A LOW FREQUENCY BUFFETING THAT INCREASED WITH ACFT SPEED. THE VIBRATION WENT AWAY WHEN THE POWER WAS REDUCED. THERE WERE NO INDICATION ISSUES. AFTER DECIDING TO RETURN TO ATH FOR MX, THE CREW EXPERIENCED A SIMILAR BUFFETING SOUND WHILE IN A HOLD & IN LANDING CONFIGURATION. THE ISSUE OCCURRED AT BOTH LOW & HIGH SPEEDS. THE FLIGHT LANDED WITHOUT INCIDENT WITH EMER EQUIPMENT STANDING BY. MX FOUND ON THE RT AIR CONDITIONING BAY CLAMP LOOSE ON RT & PACK HEAT EXCHANGER OUTLET DUCT PORT. DUCT CONNECTED & PROPERLY SECURED.