I ran into a problem that has me stumped. After 15 years, the faucet in my fiberglass shower unit needed replaced. After much searching, I finally found one for which the valve was about the same size as the old one, only about an inch wider. For the old one, the water lines came up from the floor and attached to the valve but the lines were free standing, i.e., not secured to the wood bracing. The new one, being an inch wider, put the lines against the bracing so I simply secured them to the wood as shown in the attachment (looking up at the valve). The valve is a quarter-turn valve starting at cold and opening to hot. When I begin opening the valve (cold) there is no problem. If I open int entirely to hot, there is no problem. But when I open it half way (warm), everything begins vibrating wildly. Does this indicate a bad valve, or should I not have the lines against the wood, or do I need to brace the wood better? Any help would be appreciated.