Forearm pain when preacher curling

I've noticed over the past couple of weeks that after finishing a set of preacher curls that i feel a pain in my forearms. When i let go off the bar after racking i get a minor pain in my forearms, specifically the bones? It feels like something twisting back to normal. I know the forearm bones pass over each other when turning the wrist but is this normal? For reference I'm doing around 35kg/78lbs for 7 failure with elbows slightly flared on the pad