Brent had me try just using the High-Level input - no such luck unfortunately. Did find out that adjusting the crossover setting on the sub does affect the "loudness" of the rumblings though (40 - pretty quiet, as you turn it higher the crazier the rumblings become)... and yeah, really does kinda seem like a charge is building up. Left Axiom a message as well with my number smile

*waits patiently*