ENVE Silca Valve Extender
My road bike has ENVE SES 4.5 AR Tubular wheels (from Wheelbuilders.com). I noticed a clicking noise from my front wheel each time the valve stem was at the lowest position. I determined that the extended valve stem was the source of the noise. The ENVE Silca Valve Extender was the perfect solution. No more metal tapping on my carbon rim! I highly recommend these valve extenders, even if you don't have the same issue. They will protect your expensive carbon rims from any damage a metal valve extender might cause.