Help, Phantom Distortions and Stumped Again

Another weird audio mystery...why does this always happen to me?

Friday there is a very unpleasant distortion coming from the midrange on one of my speakers and, to a much lesser extent, the other one as well. Thus ensues the lineup of the usual suspects. No on the CDP, the preamp, clean all the connections, then switch the channels and even run the speakers on another system entirely and the distortion remains the same – looks like a bum driver (and it's the finicky Thiel coaxial, so I figure that's my culprit). Sounds simple, right? But wait.

The amp in question is a Bryston 4b-st that has been having trouble with its muting switch. Which is to say that, at power down, it bleeds current into the speakers, prompting them to do a rather nasty crackling routine. Not good. So, I figure it was the amp that damaged the midrange driver. Again, sounds simple, right? But wait.

Sunday I decide to try again (with the speakers still in the second system - the Bryston is officially sidelined until it gets back from the doctor). Perfect. No distortion, no problem. To add insult to injury (or the lack thereof?!) without all of the tubes and tweaks, running off of a Marantz HT receiver and a DVD player, the Thiels sounded pretty good. Not great, to be sure (OK, a lot less than great) but a lot better than I expected.

What gives?!? The best I can come up with is that the amp may have left some lingering nasty charge in the midrange driver that produced the distortion, even while running off of a completely different amp (is that even vaguely possible?). However, couple of days later, the charge has dissipated and the driver is healthy again...? Any thoughts? (I'm not making this up, I swear...).
PS -- posted a similar inquiry to the good folk at Bryston. We'll see if they have any insight on this one and compare notes.
C'mon, Mezmo...a pistonic driver can't store that much energy! Even if you somehow overheated the VC so that there's a scraping going on due to non-coaxial movement it should clear up within a few minutes cooling.
(Brings to mind the old trick of reinstalling woofers upside down to counteract years of gravity tugging on the hanging vc....) Good luck. Ern
Beats me.... It did clear up though, the Bryston is scheduled for its checkup, and I guess that's that. It still strikes me as weird.