ACR MLG MADE A TKOF WITH THE NOSE GEAR DOORS OPEN AND DISCONNECTED FROM THE ACTUATOR.

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MAINT ARRIVED AFTER EXTERIOR ACFT PREFLT; DURING COCKPIT PREFLT; TO PERFORM MAINT REQUESTED BY PREVIOUS COCKPIT CREW (SCRATCHY EXTERNAL INTERCOM SOUND QUALITY). THEY TOOK COCKPIT LOGBOOK AND JUST BEFORE PUSHBACK; RETURNED LOGBOOK TO COCKPIT WITH INTERPHONE WRITE UP SIGNED OFF. ON TKOF LEG; FOLLOWING GEAR RETRACTION; A LOUD; PRONOUNCED; AND STEADY VIBRATION SHOOK THE NOSE WHEEL AREA OF THE ACFT. LNDG GEAR WAS REEXTENDED; AN EMER DECLARED; AND AN UNEVENTFUL TURN TO DOWNWIND AND A VISUAL LNDG ACCOMPLISHED. UPON RETURN TO THE GATE; IT WAS DISCOVERED THAT THE MAINT PERSONNEL; UPON HEARING THAT WE HAD RETURNED TO THE ARPT FOR NOSEWHEEL AREA STRUCTURAL VIBRATION; VOLUNTARILY ADMITTED THAT THEY HAD UNLOCKED THE NOSE WHEEL DOORS TO GAIN ACCESS TO THE WHEEL WELL IN ORDER TO PERFORM INTERPHONE MAINT PROCS AND HAD FORGOTTEN TO CLOSE THEM EVEN THOUGH THEY HAD SIGNED OFF THEIR MAINT PROC. SWIFT DISCIPLINARY ACTION WAS TAKEN ON THE MAINT PERSONNEL. THERE IS NO WAY TO TELL IF SUCH A CONDITION EXISTS FROM THE COCKPIT! ALL INDICATIONS WERE NORMAL EXCEPT FOR THE BUFFETING AFTER GEAR RETRACTION! GEAR DOOR LIGHTS ARE ONLY FOR MAIN GEAR DOORS. EXCEPT FOR THE CONFESSIONS OF THE MAINT PERSONNEL; I SUSPECT THAT THE COCKPIT CREW WOULD HAVE INITIALLY BEEN SUSPECT.