Turning off the rumble filter should raise the level of low bass, which makes me think you are not over driving the speakers if the rattle then disappears. The rumble filter is probably making enough of a change in the resonance of the speaker to have an effect on the "rattling". Without hearing it myself, I can only guess something is loose in the speaker. Is that what it sounds like? I wouldn't suspect a problem with the pre-amp from what little I can tell from here.