How to control long decay of B&W woofers ?

I have B&W Matrix 800 speakers (3-way system) with two 12" woofers per side. Currently the speakers are actively bi-amped between the woofers and the midrange modules using active crossover. A pair of KRELL FPB 350MC are directly connected to the woofers without the passive filters. The bass output is extremely good, deep and very tight. But some times I notice that on some drum beats the woofers don't stop as it should be, instead the woofers continue to make sound till the next drum beat. The long decay time of the woofers (some times) makes a kind of continuous background sound from the woofers and the sound becomes muddy. On many other recordings, the drum beats stop and start very accurately and the sound is very clean and crispy.

I am wondering what is the reason of this long woofer decay time (with some recordings) and how can I achieve a clean sound from the woofers ? I have tried the amps with damping factor upto 10,000, and the result is the same. Any suggestions from experienced inmates ?
Best regards,
Sunny