You can get the battery pack out by unscrewing the pommel (bottom part of the saber) and then gently shake the pack out until you get a grab on it. Then try repositioning it. Be careful when removing and reinserting the pack, you don't want to damage the wires!
I've got the batteries out and they're charging but adjusting the pack didn't seem to make any difference. I see a plug in on the circuit board though. Is there something I could do with that? I thought I heard that did something with the sound.
UPDATE: charging the batteries and moving around the battery pack didn't help at all