If it's a clicking - it could be a number of things. Need more info.
High pitched whine - gears, if so, you are fucked.
Quiet like, rapid whizzing - motor engagement, look at the bottom of the grip, there's a 1mm hex screw. Get an allen wrench and turn the screw in until the gun starts firing, and then continue to turn it until the whining noise goes away and it sounds fluid.
If it's something else, I dunno.
Battery charged?
HTH