Repeated "ka-thunk" sound when adjusting climate control

My 2005 Ford Explorer XLT started, one day about a year ago, making a “ka-thunk ka-thunk ka-thunk” sound when the temperature was adjusted drastically. For example, I turned the knob from the blue (cold) setting all the way to the red (hot setting) and tried to turn on the blower only to hear this repeated and loud “ka-thunk” and to receive (of course) no heat.

After some fiddling, I found I could oh-so-gradually work the temp up (over the course of about 20-30 minutes) to a hot setting, though definitely not the hottest. I’ve been able to adjust my own habits to live with the problem mostly with success. On occasion, I can’t adjust the temperature at all, even if I manage to turn the knob without the “ka-thunk.” These days, the" ka-thunk" only happens with a sudden attempt at a drastic change in temp OR when cranked that extra tiny bit to full heat, though I do still get a kinder, gentler version of the “ka-thunk,” the “ka-lick.”

I can usually make the noise go away by shutting off all climate control but sometimes it still occurs and won’t go away unless I turn the ignition off.

I’d hate to be having a problem that will become enormous later. Thoughts?

The problem is probably with the blend door actuator. Common problem with Ford SUV’s

Here’s a video of the problem.