My Triton Opal shower has water pouring from a plastic pipe?

Pipe is behind shower hose. In shower when it ran hot then cold, then hot, etc., and water started coming out of plastic pipe as well as shower head. New hose six months ago and new shower head more recently. So no kink or limescale. Hose also discharges a lot of muck. Is it just the PRD? Any help appreciated!