Contact Velodyne. In my experience, they're very helpful.
Dear Morgoth360: I have the same trouble with one of my HGS-15 and the problem was in the subwoofer amplifier.
I can't fix it and made contact with Velodyne and send it the rear/back plate where the amplifier is mounted and they send me a new unit!!
So, like Dbphd posted,: contact Velodyne.
regards and enjoy the music,