ACFT DAMAGED -- ACR STARTS ENGS AND ROLLS FORWARD INTO A GND VEHICLE.

Narrative

ACFT (DC-9-31) WAS SCHEDULED TO DEPART ILN XA06 TO DSM WITH AN INTERMEDIATE STOP AT CID. ALL PREFLT REQUIREMENTS WERE COMPLIED WITH INCLUDING WT AND BAL AND THE 'BEFORE START CHKLIST.' BOTH ENGS WERE STARTED. WHILE THE FO WAS COMPLETING THE 'AFTER START' CHKLIST. I WAS VISUALLY ENSURING THAT NO OBSTACLES WERE IN OUR INTENDED TAXI PATH. BEFORE WE INTENDED TO START THE TAXI; THE AIRPLANE HAD STARTED AN UNINTENDED AND UNNOTICED SLOW ROLL FORWARD; AND AFTER A GND ROLL OF PLUS OR MINUS 5 FT CAME TO A STOP AGAINST A VAN WHICH HAD BEEN PARKED CLOSELY FORWARD AND TO THE R OF THE PLANE. THE FO HAD BEEN AWARE OF THE POS OF THIS VAN; BUT BECAUSE WE WERE NOT YET GIVEN THE ALL CLR SIGN FROM GND PERSONNEL AND WE HAD NOT YET INTENDED TO START OUR TAXI; IT WAS AT THAT TIME NOT IMPORTANT. ALTHOUGH WE BOTH (FO AND CAPT) ARE SURE THAT THE BRAKES WERE SET PRIOR TO ENG START; WE NOTICED AFTER THE INCIDENT THAT THE PARKING BRAKE WAS RELEASED. AFTER GND PERSONNEL DISCONNECTED FROM THE FLT INTERCOM AND IN ANTICIPATION OF THE NEXT PHASE (IE; TAXI TO THE ACTIVE RWY) I MUST HAVE INADVERTANLY RELEASED THE PARKING BRAKE. THE ONLY DAMAGE TO THE PLANE WAS A CRACKED RADOME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ONLY DAMAGE WAS TO THE RADOME AND THE CAPT RPTS THAT IT WAS CHANGED AND REPAIRED. THE FAA DID INVESTIGATE; BUT DECIDED TO ALLOW THE COMPANY HANDLE THE CORRECTIVE ACTION. NO INJURIES AND MINOR PROPERTY DAMAGE.