Subwoofer Popping

Can someone help me?  5.1 system.  My set-up: Marantz SR6015 receiver.  Four Bowers and Wilkins 705 S2's for the R/L and rears and the B&W HTM71 S2 center channel.  All speakers set to small.  The REL T/9x is my sub.  Marantz is set to LFE + Main.  Crossover setting on the Marantz is at 80HZ.  I have tried for many months to get my settings right on my set-up but it seems no matter what I do my sub often makes a snapping/popping noise when trying to play LFE at a high volume when watching movies with the family.  It's as if something is set too high and sending too much power to the sub.  What settings do I have wrong?  For the life of me I can't figure out how to adjust everything correctly on both the sub (the phase, HI/LOW LEVEL, CROSSOVER, and the .1/LFE LEVER) and the various settings on the receiver (crossover frequency for the REL, subwoofer level adjust,