I just replaced my shower/tub faucets and had to replace the valve. A few weeks after replacing the valve the shower has randomly made a very loud vibrating sound. The shower is used daily and it only happens about once or twice a week. It starts about a minute or two after turning the shower on. It stops as soon as I turn the water off and when I turn it on again its fine for another few days. The new valve was bigger than the old one so the hot water pipe is resting against the stud. Could it be that the pipe is just vibrating off it? There was also some solder that came out the tub spout the first few days. Could there be some stuck in the shower pipe or the valve?

Something's vibrating in your shower valve. Turn the water off, open it up and turn the water back on to flush it out. Good luck, Tom.