In a message dated 1/30/2013 10:30:14 A.M. Eastern Standard Time,
asonder@USGS.GOV writes:

On the  freeway this morning the passanger side rear wheel clunked like I
hit a  rock.  It happened 2 more times.  Got off freeway to examine  tire.
Pressure around 45 tire, looks normal, grab and shake-no give.   The belts
look o.k.    Drive the backroad the rest of the way to  work for lower
speeds and i happened again 2wice.   What could be  going on?

check cv axle?