Turntable sounds so much better when...

Absolutes are never absolute, simply conveniences.  Hi-end is subject to brainwashing and group think the same as any other facet of culture, big or small. As example, it is true that metal platters ring, but a good engineer designs a TT to channel the ring to the feet, and not smear the sound.  Good quality perspex does not magically make a clear sounding TT, the whole thing has to be designed to work with the platter of choice. there are good sounding TT with both materials; no absolutes. Check everything for yourself--surprises abound. In this case, I would agree you have de-coupled resonance. Good luck and have fun!!!

Many interesting thoughts here in the posts above.....the whole time I was reading I was thinking about the late Tom Fletcher, who many of you know was the originator of the Nottingham Analogue Studios fine line of turntables (of which I am fortunate to own one), who believed the issue of "tight" was important enough to mention in step 1 of his set up tips in the dealer manual:  "You should tighten just enough to hold in place," referring to all the "little screws, grubs and bolts when setting up a turntable." His perspective on over-tightening was that "this will raise the frequency of the turntable thereby exaggerating surface noise and making the table bright and strident." 

OP, it may very well be that your relaxing the tightness between your headshell and tonearm goes directly to this part of his commentary.....I know that it makes a noticeable difference on my TT.....took me a while to source that dealer manual, but once I did and carefully digested it, I went about re-tightening (read as "loosening" a bit) all the various screws involved and found the sound to open up quite a bit and become far more pleasing. 

Just passing along some of the knowledge I've discovered after nearly 6 years of owning this very wonderful TT although I have also noticed some challenging idiosyncrasies that are yet to be solved.....getting to know your TT is part of the joy, in my opinion, especially when you find aspects that contribute to what your ears tell you is "better" sound!  And it certainly appears that you have made such a discovery.....listen on, and bask in the beauty of what you hear!

All that said, I would also echo some of the other posters who suggest that this procedure likely affected your cartridge position/setup in a happy way......it would be interesting for you to get some really top-notch alignment tools and compare what you get with the cart in the present, desirable position to the outcome upon tightening it as it was before your "aha" moment!  Have some fun and let us know if you perform this test.

Advocating for something your Passionate about is Easy..
Getting others to see your point is sometimes Difficult! Richard Dunn

I've got a screw loose and I'm feeling great!

"I've got a screw loose and I'm feeling great!"

And you probably sound really, really good too!!!