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Was that the first time you moved your cables in some time? this would -could effect sound quality because if your cables have not been moved in a long time your basically reseating the cables and cleaning off the corrosion and making a better connection. always remove your cables periodically for this reason. Also before you evaluate new cables reseat you old ones first so your not taking in the cleaned contact surface as the new cable sound.
one thing we don't seem to think much about is contact corrosion from dissimilar metals (silver and copper, copper and iron for example). also copper corrodes quite fast on the surface.
It could just be that all the turning has cleaned off some contacts somewhere.
I do find that the harder the materials used in the binding posts and spades, the worse a connection you get. Tightening them down doesn't seem to help. Softer materials in the screw threads, spades or binding posts tend to work better.
Otherwise, it is possible there was some physical resonance happening that went away with the loose screws.
@glennewdick and @erik Thanks for replies but I can assure you if that was the case I would not start this thread. I plugged my cables thousands of times since, cleaned the posts and always made sure from time to time that the posts were solid ( but not overtightened ) for such replies I write in advance - no such things like neglecting something. Not touching for ages etc, please calculate this out.