I agree with Erik having found a loose spade or two. I will second locking bananas as the best solution and one that I believe bumps up the surface area in contact with the speaker. The spade issue has always stuck me as something fairly easy to fix with a spring or lock washer, but then there will we will need 7n OCC gold plated versions of those too.
Bananas rule, spades drool. End of discussion.
I just checked my speaker connections. All using bananas, all nice and tight.
The number of times I’ve had spades get loose instead though.....
Point is, and it really is kind of a tongue in cheek thing, bananas beat spades for long term reliability in almost all setups. If you have to use a Cardas or Mundorf speaker terminal to ensure your spades stay tight it kind of proves my point.