Heater Valve on F10 concern

[AlpineF10]

I have this exact problem below:

The "knock" is caused by a rhithmic vibration of the heatervalve that appears every few seconds. It does that only when the blower is on, within certain temp limits, regardless of the fan speed, engine revs, or if the a/c is on. The knocking does not occur when the temp is set to 16C/60F (the valve is completely shut) nor when the temp is set to 32C/91F (the valve is fully open), only within a rather narrow, variable temperature range in between.

Despite the disturbing knocking, the temperaturecontrol works fine. Needless to say, the engine does not overheat, there are no coolant leaks, etc. What's puzzling me most, the valve continues to knock even after the engine is turned off, provided that the blower on (by keeping the key in accessory position). That means the knocking is not dependent on coolant circulation."


Does anyone else have this issue? if so, how do I fix this problem?