Originally Posted by
cyccommute
I suspect that you have a cracked rim. Either at the eyelets or, if you remove the rim tape, around the spoke holes.
+1 This would be my guess, too. If possible get a Sun CR-18 rim as they're cheap/strong and have your lbs build a new wheel using the old hub and DT Alpine 3 spokes. A Mavic A719 would be better, but 2-3 times the money. You may be running your tires @ too low psi which will lead to rim cracks, truing issues, etc. given the description of your terrain.