B737-900 CREW RETURNED TO THE DEP STATION WITH AN ELECTRICAL ACCESS DOOR THAT WAS NOT CLOSED.

Narrative

DURING CLB; WE FELT A VIBRATION AND HEARD A STEADY 'HUM' FROM THE LOWER COCKPIT AREA. I SUSPECTED IT WAS THE EXTERNAL PWR ACCESS DOOR THAT MOST LIKELY WAS NOT CLOSED PROPERLY. (THIS WAS INDEED THE CASE AFTER WE RETURNED.) OUR WORKLOAD WAS VERY HIGH AS WE WERE NAVING AROUND TSTMS AND DEALING WITH A HIGH VOLUME OF ATC TFC. I ELECTED TO RETURN TO ZZZ AFTER APPROX 15 MINS FROM DEP. I CALLED ZZZ OPS AND ASKED THEM TO NOTIFY DISPATCH AND MAINT OF OUR RETURN AS WE HAD NO TIME TO CONTACT THEM DIRECTLY. AFTER OUR RETURN TO ZZZ; I CALLED DISPATCH ON THE PHONE TO DEBRIEF AS WELL AS OBTAIN AN AMENDED DEST TO OUR RELEASE. I WAS INFORMED THAT THE FLT HAD ALREADY BEEN 'CLOSED OUT' IN THE COMPUTER AND THERE WAS NO WAY TO ENTER THE AMENDMENT (CHANGE OF DEST). IT WOULD SEEM TO ME THAT THIS SHOULD BE DONE AUTOMATICALLY BY DISPATCH WHEN FLT CREWS HAVE NO TIME DURING HIGH WORKLOADS SUCH AS THIS. WE DID NOT DECLARE AN EMER AS WE FELT IT WAS UNNECESSARY. THE DISPATCHER I WORKED WITH WAS VERY HELPFUL AND COOPERATIVE AND AGREED THAT A BETTER SYS OR PROGRAM SHOULD ADDRESS THIS.