Linear Profile Bearings - Clatter Noise, Maintenance?

[JAZZCNC]

Also I suppose you have to wonder why they are second hand, were they knackered and they replaced them or was the equipment using them retired.

I've bought loads of used rails and mostly they are perfectly fine. Infact the X axis rails on my machine where Second hand 6yrs ago and they are still fine, an trust me i've abused them badly.
The Y & Z axis are SBC fitted new 6yrs ago and again run and abused in some pretty shity conditions and they are still like new with no signs of wear so i'd be very surprised if it's anything other than something simple like the plates.

Also realise These type of rails don't float on air like lots of people think or expect and they have a preload which can give the impression they are sticking or binding. Some noise is not unusual but this does sound like catching plates.