My '02 Explorer has developed an clicking sound in the rear end of the
vehicle. The best way I can describe the sound is that it sounds like
turning a child-proof medicine bottle top without pressing down on it.
The noise is intermittent and can be heard both when braking or driving
at a constant speed. (I think I may notice it more when braking because
of less ambient noise.) It doesn't seem to be related to any one action
(acceleration, deceleration, transmission shifting, etc.) and I haven't
noticed any change in vehicle performance. Has anyone else had this
problem or know of what could be causing this?

Thanks in advance,
Joe