SuperCube III Rattling

Just purchased a Supercube III for my HT setup.

Watching the Halo3 Announcement trailer on the 360 was the 1st think I tried. The woofer rattles whenever a bass note hits in the beginning.

Seems to rattle whenever the sub is up over 25% power.

Sub is in an open environment with it's back 3" away from a wall.

Connected to Denon 1909 via LFE, volume around -38dB.

Have already run the Audessey auto-setup. Is it something wrong with the crossovers? What am I doing wrong?

Thanks!

Found another thread and it looks like the Audessey auto-calibrate jacked my sub settings. Switched to manual settings and it seems cool now.