I have a hand held shower head installed and after showering there is a howling noise coming from water lines/plumbing in the bathroom. It just recently started and I am not sure what is causing this. Any ideas?

This noise comes AFTER you shut the shower off? Do this. Lift the toilet tank lid. If the water level is any where above 1/2 inch from the top of the white overflow tube reset the level back down. Let me know if it helps.