Muscle cramps/locking

Been having this for a while now. Both my tricep (inner head) and brachialis radi in my left arm tend to spontaneously cramp into a locked position. The muscle belly shortens and bulges without the arm being flexed (or extended). Very damn painfull and annoying. Any ideas?

I got this during the loading cycle of creatine cause I was not drinking enough water. Hydration is very important.