subwoofer kicking off and on during dialogue

[RedZeppelin]

Hello. I recently had to purchase a new subwoofer for my home theater system. I purchased a Paradigm Defiance V10, and I'm running it from an old Yamaha RX-V373 5.1 receiver.

I didn't do any assisted calibration; I just set it to what sounds good, and it sounds fantastic.

However, during dialogue in films and TV shows, I can hear the sub kick in in the middle of a sentence, like it dropped out briefly and something finally re-engaged it. I usually don't even notice when it disappears, because it never drops out during loud scenes or scenes with constant bass. But suddenly in mid-sentence I'll hear the nice bass floor reappear, letting me know it was off for a time.

I did some research and saw frequent suggestions to change all my other speakers to small in my AV setup, which I did. That seemed to help a little but the problem is still there.

Any suggestions?

Thanks.