I had an odd one today, sort of in the vein of the "some days are worse than others" thread.
Mine probably is not as serious as ones discussed there, but while I was machining out some small nuts from AL, I started hearing a really god-awful noise coming from the spindle area. Sounded like someone was beating on the spindle with a hammer, so I was sure my bearing were toast.
When I opened the door I found that the large bolt on the PDB that engages the draw bar from the bottom of the cylinder had some how vibrated loose and when it touched the draw bar it started unscrewing itself. This was pushing the cylinder up and eventually over and off the eccentric nut then to the side, hence all the noise.
Simple enough to re-tighten the bolt, and no real damage. but just thought I would pass a tip to everyone who has a PDB to maybe check that bolt for tightness every once in a while.
Terry