subwoofer distortion

I have a Talon Roc 2002 subwoofer.  It’s a beast w/ 2 12" drivers @125 lbs w/ a 1000w Bash plate amp.  For the last 10 years, it hasn’t distorted - until now.  What’s changed is cleaner power and better cabling throughout the system.  With a double bass or electric bass guitar, there’s no distortion.  With pounding kettledrums or an electronic synthesizer that goes subterranean, the sub breaks up.  Will the distortion damage the drivers?  Is this a design flaw?  Any solutions? Thx.
This "distortion" sounds like too much excursion. If ported, consider sealing it.

Yes, it can be damaging.
Excursion limits is most likely the issue, it could certainly be amplifier clipping... These big peaks suck huge power.  You may consider dropping gain a bit to the sub if your system will tolerate it. 
Overall, I would not seal the box.  You would dramatically change the bottom end frequency roll off and the woofer would be probably be in too large of a box for sealed design... I say probably, not definitely. 
In every case, when you put a woofer in its optimal and perfectly tuned sealed box... that woofers optimal perfectly tuned sealed box will be a smaller box, the perfect thought of QTC of .707 would drop in a larger sealed box,  BUT, you can easily tune a woofer for good performance in smaller boxes and frequencies can be permanently eq'd in built in amps... So "Probably"... The good news is that trying it is free, it won't hurt the woofer to try it.
I hope this helps,
Sorry,  Mis quoted myself... " In Every Case, when you put a woofer in its optimal tuned ported box, that woofers optimally tuned sealed box will be smaller" 
I suggest to replace the cables to the old ones you had and to check if the distortion in your sub is still happening ,I suspect the new cleaner power and cabling  have somthing to do with that.
Curious about this too as this has happened to my B&W ASW800. In my case I upgraded from receiver to balanced pre-pro., using the same cabling to the sub.
You changed something, now it distorts. Correct? Change it back.....
most likely drivers damaged it is 15 years old and a sub most likely surrounds going I would check and repair before I use more since you could or already may have damaged the VC
Your responses prompted an investigation.  The short answer is that the gain on the sub was too high. The cleaner power and better cabling greatly improved my system’s resolution, top-to-bottom.  What I didn’t anticipate, was how articulate below 30Hz would become – and the sub’s ability to deftly deliver it.  Also, I was listening at a louder volume since the music sounded so good.  Upon subscribing to Tidal, I started listening to a far wider variety of offerings – some of which went much lower than a typical double bass or electric bass guitar.  This is when distortion was revealed.  It seems that what was working before, didn’t any longer with the improvements.

The solution.  Re-positioning the sub.  A friend came over last night to help move this 125lb beast. We moved it about 4ft from its previous position.  Then spent considerable time dialing in the cross-over and volume.  All is good again. Sounds really nice.  Also, I read an old review where the manufacturer recommended a certain interconnect specifically designed for subs – an Analysis Plus Sub Oval.  Even though the distortion is gone, I ordered the IC.  Will report back.  Thx for the help!