[Alpine5x]

Hi I have this problem where I hear a faint knocking on my 2013 BMW 528ix. Hope you guys can assist

The "knock" is caused by a rhithmic vibration of the heater valve 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).

Despite the disturbing knocking, the temperature control 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 accessoryposition). That means the knocking is not dependent on coolant circulation."

Any solutions?

[BuiltnBoostedZ]

The heater control valve shouldn't be doing this at all. Its either open or closed. Rhythmic vibration doesn't make a whole lot of sense to me. This is a valve that's electronically controlled by a solenoid to open and close depending on what temp you set the AC to. I'm willing to bet something in the valve is jacked up and making the solenoid constantly move it back into the correct position. I'd change it out. Should be fairly easy to do. The only challenge in changing something like this yourself is the coolant aspect. You don't want to get any air in the system or you'll be doing things twice. When done installing, add coolant and burp the system.

Depending on how many miles you have, you might check all support parts for this part of the heater/coolant and/or change the coolant out. That will give you some extra insurance for a longer part life.

[Alpine5x]

what exactly should I be replacing? the water valve?

[BuiltnBoostedZ]

Yea, the valve itself. The part with the solenoid attached. You should be good after that.