ACFT MECHANIC WAS IN THE COCKPIT OF A320 TO APPARENTLY INVESTIGATE A BRAKE PROBLEM. WITHOUT WARNING; HE RELEASED THE PARKING BRAKE AND THE ACFT ROLLED FORWARD.

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WHILE IN COCKPIT FINISHING PREPARATION FOR DEP A MECH CAME TO THE COCKPIT AND WITHOUT SAYING A WORD BEGAN GOING THROUGH ECAM PAGES. I ASKED WHAT WAS WRONG. HE SAID HE WAS LOOKING AT A BRAKE PROB. I ASKED THE FO IF HE HAD NOTICED ANYTHING ON THE WALKAROUND AND HE SAID ALL WAS NORMAL. THE MECH ASKED ME TO PUMP THE BRAKE PEDALS. AS I TURNED IN MY SEAT TO DO SO THE MECH RELEASED THE PARKING BRAKE WITHOUT ANY WARNING OR INDICATION THAT HE WAS GOING TO DO THIS. THE AIRPLANE MOVED FORWARD ABRUPTLY. I WOULD SAY IT MOVED ABOUT 6 INCHES. THERE WAS A LOUD BANG FROM BELOW THE PLANE. I COULD NOT TELL EXACTLY WHERE IT CAME FROM. I RESET THE BRAKE IMMEDIATELY AND ASKED WHY HE HAD DONE THIS. HE GAVE ME NO ANSWER. I TOLD HIM WE HAD TO SEE IF THERE WAS ANY DAMAGE OR INJURY. HIS RESPONSE WAS THAT HE WOULD CHK WHEN HE WAS DONE. I WENT TO THE RAMP TO CHK FOR MYSELF. ONLY THE NOSEWHEEL WAS CHOCKED. IT WAS NOT AGAINST THE CHOCKS FRONT OR BACK. THE TUG AND TOWBAR WERE ATTACHED. I SUSPECT THE PLANE TOOK UP THE SLACK IN THE TUG/TOWBAR/NOSE GEAR CONNECTION WHEN IT MOVED. LOADERS WERE IN EACH CARGO PIT; BUT HAD NOT HIT ANY PART OF THE PLANE. THE RAMP PERSONNEL ALL SAID THEY WERE OK. THE MECH LEFT WITHOUT TELLING US IF THE PROB WAS RESOLVED OR EVEN WHAT THE PROB WAS. WE FINALLY CALLED MAINT TO SEE IF WE NEEDED A NEW MAINT RELEASE. HE DID NOT KNOW A PROB WAS BEING WORKED. I THINK WAS A VERY DANGEROUS SITUATION WITH A HIGH POTENTIAL FOR INJURY OR DAMAGE TO THE ACFT.