I wouldn't call it normal, but it may not be bad either. I'm just not sure. Mine don't do it, at least not that I notice anyway. Could it be your tort is clicking his jaw for some reason? Perhaps he is scared or trying to show domination?
Hopefully someone with more experience will chime in soon.
We get this question a lot. Turtles can make a clicking/croaking sound by grinding their upper and lower beak together. No one's really sure why they do it (could be just to clean their beak, could be a form of communication), but it's called stridulation, and it's perfectly normal.