X-pole moving / rotating

Hi, My one of the poles in my x-pole (x-pert) is rotating slightly. I've only used it on spin-mode once and it was fine after we put it back on static mode. But recently, the pole seems to rotate slightly... so basically, when i do an inversion, the pole rotates and makes a sound. i don't think the pole is going to fall, or that it's necessarily going to suddenly switch to spin mode. Nonetheless, it's a bit disconcerting and distracting when for the pole to turn when i'm learning new tricks. I've tried tightening all the joints/nuts - whatever they are called - the two sets connecting the two poles in the middle, as well as the two sets right at the bottom of the pole; and i've tried loosening them and retightening them again, but it's still moving. could someone please advise? x