What was found
DURING TAKEOFF, CREW FELT A VIBRATION IN THE AIRCRAFT. ONCE AIRBORNE, THE VIBRATION CEASED AND THE LANDING GEAR WAS RETRACTED. AT THAT TIME, A LANDING GEAR DISAGREE MESSAGE, ALONG WITH A GROUND SPOILER MESSAGE WAS GENERATED. THE LANDING GEAR MESSAGE WENT AWAY, BUT THE GROUND SPOILER MESSAGE DID NOT. FLIGHT RETURNED TO THE FIELD, AND UPON GEAR EXTENSION, DID NOT RECEIVE A GEAR DOWN AND LOCKED INDICATION. THE FLIGHT PERFORMED A FLY-BY OF THE TOWER, AND RECEIVED CONFIRMATION THAT THE GEAR WAS DOWN. SINCE THE GEAR COULD NOT BE VERIFIED -LOCKED- THE CREW INITIATED PROCEDURES FOR A PARTIAL GEAR UP LANDING. AFTER BURNING 45 MINUTES OF FUEL WHILE HOLDING, THE FLIGHT LANDED IN IAH. VIBRATION OCCURRED AGAIN DURIN