What the H ll Happened Here?

I was listening to music two nights ago and heard what sounded like low level scratching through one speaker, then it went away. A short while later it happened again but this time the sratching was coming from both speakers with reduced bass response. Then, I lost bass in one speaker completely with maybe 1/2 output from the other. Tweeters seem OK but hard to tell as they sound kinda bad without the rest of the spectrum.

By the way, I have Harbeth C7s which are two ways.

I thought the problem may be tubes in the pre-amp so I plugged in a passive that was just boxed away, same problems. Tried another amp, CD player (with and without the DAC), same problems. Swapped speakers from side to side, problem with woofers went with them. Then I tried pressing slightly on the woofers, doing so causes changes in the distortion. So I'm pretty damn sure it's a problem with both speakers, but what the hell happened? And to both speakers at the same time?? I noticed no electrical surges, power problems of any kind.

Guys, any ideas as what's going on???