I have a shower tub combination. All of a sudden when I open the hot water for the tub it moans and groans like a ghost in the walls. When I divert to the shower it stops so it isn't a pipe rubbing on the strap. Nothing happens on the cold water tap. I replaced the springs and bushings on the valve last night as directed by my plumber, however, it persists in singing and whinning. What is it and how do I fix it?