Narrative:

During climb out; we began to notice a high frequency buss/vibration after climbing through 10000 ft. The vibration/noise began to get more pronounced above FL180 so we leveled off at FL230 to troubleshoot the problem. Slowing the aircraft did not have any applicable effect on the noise or vibration level. We determined that either the nose gear door had not secured flush after gear retraction or that the external power receptacle door was not secured and extended into the wind stream. Climbing and accelerating to cruise altitude was not an acceptable alternative so we chose to divert to ZZZ to have maintenance investigate the issue. An emergency was declared for expeditious handling. Upon arrival in ZZZ it was discovered that the external power receptacle door had not been properly secured prior to departure.

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Original NASA ASRS Text

Title: AIRFRAME VIBRATION ON B737-700 RESULTS IN DIVERSION FOR MAINT INSPECTION.

Narrative: DURING CLBOUT; WE BEGAN TO NOTICE A HIGH FREQ BUSS/VIBRATION AFTER CLBING THROUGH 10000 FT. THE VIBRATION/NOISE BEGAN TO GET MORE PRONOUNCED ABOVE FL180 SO WE LEVELED OFF AT FL230 TO TROUBLESHOOT THE PROB. SLOWING THE ACFT DID NOT HAVE ANY APPLICABLE EFFECT ON THE NOISE OR VIBRATION LEVEL. WE DETERMINED THAT EITHER THE NOSE GEAR DOOR HAD NOT SECURED FLUSH AFTER GEAR RETRACTION OR THAT THE EXTERNAL PWR RECEPTACLE DOOR WAS NOT SECURED AND EXTENDED INTO THE WIND STREAM. CLBING AND ACCELERATING TO CRUISE ALT WAS NOT AN ACCEPTABLE ALTERNATIVE SO WE CHOSE TO DIVERT TO ZZZ TO HAVE MAINT INVESTIGATE THE ISSUE. AN EMER WAS DECLARED FOR EXPEDITIOUS HANDLING. UPON ARR IN ZZZ IT WAS DISCOVERED THAT THE EXTERNAL PWR RECEPTACLE DOOR HAD NOT BEEN PROPERLY SECURED PRIOR TO DEP.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.