Funky heater control valve

[RIboater2]

I have heat, no issue there. But one of the valves cycles on/off every 3-4 seconds. When just sitting at idle you can even hear it inside the car. Do you think it would be a defective coil in the valve or something external telling it to cycle on/off?

[Timm]

They do cycle ON/OFF at regular intervals once up to operating temperature - but excessive noise usually means a worn one