While this is a large sub (300W, 45lbs), it is not really capable of going that low. You may indeed have pushed your sub too far. I f you have a powerfull amp (100+ Watt), and all five channels are low-pass filtered to the sub, you could be bottoming it out. I used to have a Klipsch RW-12 sub (one of their better ones) and it was crackling all the time (I push my speakers pretty hard). I initially thought this was normal and lived with it for almost a year, until I figured out this was problematic. Once I replaced the sub with a more powerful model from SVS, the crackling was gone and I turn up the volume much higher.