Our home is plumbed with PEX tubing, from what I can tell. When summer started, the shower started running hotter, so we turned down the shower lower and lower. But when we reached a certain place on the shower dial, the water began to pulse - almost like a massaging shower head, but much slower. (In case you're wondering, yes, there is a massaging head, but it is definitely off when this happens.) If we turn the water up or down from this "goldilocks temperature" (which is of course the most comfortable temperature), the pulsing stops. Any ideas?