Originally Posted by
Andrew R Stewart
Bearings that are so dry of lube and not tightly adjusted so you can hear as the bearing that is "going over the top" you can hear it fall onto the bearing preceding it.
Can also happen when greased with very thin grease or oil, even when adjusted so there is no slack. WD-40 sprayed into bearings can make the lubricant very thin, but not dry, for example.