I've experienced something similar but it was when I was doing preacher curls with an ez bar. I think I actually pinched a nerve in my elbow on the bench. I got a shooting pain in my forearm and my pinky finger didn't feel quite right for a month.

My solution: Don't do preacher curls anymore.

Does it happen when the back of your elbow is touching something or just when there is weight on it?

IW