Check into thoracic outlet syndrome. As muscle grows it can pinch the nerves and blood vessels that flow down your arm causing shoulder pain that can seem quite a bit like a rotator cuff and numbness that runs from your shoulder, through your elbow, and into the hand. Stretching daily by holding your arm, making a 90 degree angle with your forearm, and with an open palm bracing on a door facing or corner and twisting away from your arm so you pec stretches can help out a ton if this is the problem as it is usually a pretty minor variety among weightlifters and athletes. Within a couple of days, I quit going numb. After a week, I lost almost all symptoms. I would not assume this was the problem had it not been something plaguing me for several months.
Physical Therapy Corner: Thoracic Outlet Syndrome — Portal