Crackling coming from Velodyne DD-10 subwoofer

This started as a small problem a few weeks ago whenever I powered the sub on, then would go away in about 5 seconds, and the sub would play fine. Last night, the problem worsened as the sub actually crackled and distorted with program material playing through it. It isn't constant, but occasional. I'm VERY irritated, since I didn't expect this from a Velodyne sub. I have a second DD-10, and I switched the interconnects and power cords betweem the two just to make sure it is the one sub that is the problem, and it is. Any thoughts? This started as a small problem a few weeks ago whenever I powered the sub on, then would go away in about 5 seconds, and the sub would play fine. The problem worsened and now the sub actually crackles and distorts for a brief period when turned on and intermittently with program material playing through it.