What was found
DURING CRUISE AT 24000 FT, NOTICED A LOUD NOISE ACCOMPANIED BY A CONTINOUS VIBRATION. DECELLERATED FROM 300 KTS TO 200KTS (APPROX). NOISE DECREASED BUT DID NOT GO AWAY. SUSPECT NOSE GEAR DOORS DEPLOYED PREMATURELY AS NOISE WAS MORE PRONOUNCED IN NOSE OF ACFT THAN AFT CABIN. DECLARED AN EMERGENCY AND LANDED WITHOUT INCIDENT. ACFT REMOVED FROM SERVICE. PERFORMED GENERAL VISUAL INSPECTION OF ACCESS DOOR PANELS ON ACFT. FOUND ACCESS DOOR PANELS ALL CLOSED IAW SRM 52-40-01. CHECKED NLG DOORS AND AREA IAW AMM 32-22-00, DOORS SEEM OK, NO DEFECTS NOTED IN NOSE GEAR AREA. CHECK FLIGHT WAS SATISFACTORY. THE ACFT RETURNED TO SERVICE.