Narrative:

After takeoff and on climb out, the aircraft developed a slight vibration and a loud high, pitch noise which appeared to be coming from the nose cone. Volume increased with speed. First officer and I discussed what it could be. All doors showed closed. Aircraft was pressurizing ok. I called flight attendants to inquire if they could hear noise. They could not. Source had to be somewhere on aircraft nose. We thought possibly nose gear door(south) as source. Dispatch and maintenance control were called. ATC was notified and we returned for a normal (below maximum landing weight) landing. No emergency was declared. ATC called out all crash fire rescue equipment equipment and thought we had declared emergency. Maintenance inspected aircraft and I found ground interphone access hatch to be open (push out crew had forgotten to close it or closed it incorrectly). The hatch pivots upward (not with airstream), unsafe design! I would have never guessed that a 8 inch by 8 inch hatch will create that much noise and vibration.

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Original NASA ASRS Text

Title: A CANADAIR 700 IN CLB AT 17000 FT DIVERTED DUE TO A LOUD HIGH PITCH NOISE AND SLIGHT VIBRATION CAUSED BY THE GND INTERPHONE SVC DOOR UNLATCHED.

Narrative: AFTER TKOF AND ON CLBOUT, THE ACFT DEVELOPED A SLIGHT VIBRATION AND A LOUD HIGH, PITCH NOISE WHICH APPEARED TO BE COMING FROM THE NOSE CONE. VOLUME INCREASED WITH SPD. FO AND I DISCUSSED WHAT IT COULD BE. ALL DOORS SHOWED CLOSED. ACFT WAS PRESSURIZING OK. I CALLED FLT ATTENDANTS TO INQUIRE IF THEY COULD HEAR NOISE. THEY COULD NOT. SOURCE HAD TO BE SOMEWHERE ON ACFT NOSE. WE THOUGHT POSSIBLY NOSE GEAR DOOR(S) AS SOURCE. DISPATCH AND MAINT CTL WERE CALLED. ATC WAS NOTIFIED AND WE RETURNED FOR A NORMAL (BELOW MAX LNDG WT) LNDG. NO EMER WAS DECLARED. ATC CALLED OUT ALL CFR EQUIP AND THOUGHT WE HAD DECLARED EMER. MAINT INSPECTED ACFT AND I FOUND GND INTERPHONE ACCESS HATCH TO BE OPEN (PUSH OUT CREW HAD FORGOTTEN TO CLOSE IT OR CLOSED IT INCORRECTLY). THE HATCH PIVOTS UPWARD (NOT WITH AIRSTREAM), UNSAFE DESIGN! I WOULD HAVE NEVER GUESSED THAT A 8 INCH BY 8 INCH HATCH WILL CREATE THAT MUCH NOISE AND VIBRATION.

Data retrieved from NASA's ASRS site as of July 2007 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.