Looking for new speakers

Diana Krall... almost unlistenable.

Isn't that always the case...?

I don't know if this is relevant, but...

Decades ago I owned 3.6's for a while.  Driving them with Muse 175 monoblocks.  There was one passage on one CD of piano music (Martinu) that excited some kind of ugly resonance/distortion in one of the Thiel's tweeters.  It was a metallic kind of sound.  I was never able to determine definitively if it was a fault in the amp or the speaker or the interaction between the two.  But in the long run I found the 3.6's fatiguing, so they left the building.

Finding a recording that consistently excites the problem is the first step, followed by listening to the system on headphones.  Can you say which of the drivers you hear the problem in?  I imagine you can still get tweeters etc. for the Thiels (Thiel owners thread); a lot cheaper to install those yourself than shipping the speakers.

The distortion I'm talking about is not egregious -- it doesn't immediately jump out at you, the way it might it there were serious issues with a driver or something -- in fact, close listening (with ear up to speaker) reveals that there are no drivers that are standing out as worse than others. It took me months of listening to realize that this was happening (it shows up most clearly in the Diana Krall record). In the beginning, of course, all I could hear was how much better it sounded than my old system. But over time, the sound difference from the previous system fades from memory, and you start hearing the flaws ... this seems to be the process! And one of the flaws I'm hearing is that there's just a STRAIN ... that might be a better word than distortion, though at root that's what it is .. especially in the instrumentals behind the lead voice, or the lead instrument (anywhere there's a large amount of sound coming through, as opposed to a single voice). Once you hear it, you can't unhear it!

I think maybe I should have just said I'm looking into the possibility of new speakers, and not mentioned distortion!

I appreciate all the comments and suggestions, and I will definitely check into some of the speakers mentioned.

P.S. For those who suggested speaker cables -- I am going to try upgraded cables just to make sure they are not the problem. They are all that remains of my previous system -- Purist Audio Aqueous from early 90s! Not bad but .... who knows.