EXTERNAL PWR DOOR WAS LEFT OPEN ON A B737; CREATING A VIBRATION THAT INCREASED WITH INCREASING AIRSPEED. FLT RETURNED TO DEP ARPT.

Narrative

WHILE CLBING OUT AT APPROX 16000 FT THE FLT CREW FELT AND HEARD A VIBRATION AT THE FRONT PORTION OF THE ACFT. AS SPD INCREASED THE NOISE BECAME LOUDER. AIRSPD WAS DECREASED SLIGHTLY AND NOISE SEEMED TO DECREASE. MAINT CTL WAS CONTACTED VIA RADIO AND AFTER SOME DISCUSSION THEY REQUESTED WE RETURN TO ZZZ. OUR LOCATION WAS APPROX 135 MI E OF ZZZ WHEN WE STARTED OUR RETURN. THE CAUSE SUSPECTED AT THIS POINT WAS THE EXTERNAL PWR PANEL MAY HAVE BEEN LEFT OPEN BY THE PUSHBACK CREW. WE WERE GIVEN AN AMENDED RELEASE BY DISPATCH TO RETURN TO ZZZ. OVERWT LNDG AS WELL AS GUSTY WINDS IN ZZZ WAS DISCUSSED BY CAPT AND FO. DISPATCH WAS CONSULTED; ALSO. FLT CREW ELECTED TO DECLARE AN EMER SO FIRE EQUIP WOULD BE AVAILABLE DURING LNDG. DISPATCH WAS ALSO ADVISED OF THIS. ACFT REQUESTED LOWER ALT EARLY IN ORDER TO BURN AS MUCH FUEL OFF AS POSSIBLE. LNDG WT WAS APPROX 156600 LBS WITH WINDS APPROX 190 DEGS/14 KTS GUSTING TO 21 KTS. FLAP BLOWBACK WAS A MAJOR CONCERN DURING APCH SINCE REF SPDS WERE VERY HIGH. ACFT WAS LANDED WITHOUT INCIDENT. INSPECTED BY THE FIRE DEPT AND THEN TAXIED TO GATE. MAINT WRITE-UPS WERE THE ORIGINAL NOISE AS WELL AS AN OVERWT LNDG WITH A SINK RATE UPON TOUCHDOWN OF LESS THAN 200 FPM. MAINT CONFIRMED EXTERNAL PWR PANEL DOOR WAS INDEED LEFT OPEN AND DAMAGED SLIGHTLY.