string rattle

OK, I'm serious. The last couple of weeks (NYC 70-90 degrees locally) I'm in my basement with five basses. Three in a triple stand and one each in separate single stands (all Musician's Friends stands I believe). So... once in a great while (and twice a few days ago) I hear a string rattle...

I changed my strings, The correct way, 1 by one, not removing the old ones all at once, But one at a time.NOT A DEAD STRING! I’ve never messed with my truss rod or action, but it seemed like one string was giving me a sitar effect when strummed to hard open, and on frets higher up the neck, I...