Putting a hipass xover on the interior will clean thoes up. We recomend going to a vented box. It will give you better overall sound out of the sub, compared to the limited frequency range of the bandpass box. Fianally retune the amp to get the most out of the amp. By the way is it a single or dual voice coil sub and are you bridging the 2 ch amp or running the sub off of one channel ?