I recently bought a True Sub MK II used. The sub seems to be in superb condition physically. I can't find a single thing wrong with it. The problem is this: it makes a mechanical noise, very similar to the chuffing sound ported speakers sometimes make, when playing extremely low bass. This happens even at moderate listening levels. So far I've only found two tracks that cause the sub to make this noise: "Jurrasic Lunch" from The Great Fantasy Adventure Album, and track 2 from "The Fifth Element" soundtrack. In both cases, the noise only occured in passages with content well below 30Hz. I watched "The Fellowship of the Ring" last night, at pretty high volume, and didn't notice any problems. Ditto with the pod race sequence from "Episode I". I popped the back plate off (the warranty is long since expired) and noticed nothing obviously loose or out of place inside the cabinet. I'm wondering if any of you have experienced similar problems, or if this is simply what this sub does when confronted with really deep bass. If it is a problem and you know of a fix, I would appreciate that as well. Thanks in advance!