Inter-mitten Climate Control

As I was running the truck through the car wash I noticed that my climate control was blowing air some what intermittently.

Once I got home I tried toying with other components with the climate control. A/C exacerbates the inter-mitten effect in that it makes it more noticeable because the cooler air blows intermittently as well. It's not as noticeable at lower blowing levels (makes sense), but it's still there. Cranking the climate control to full heat does make it stop tho.

Now, I drive the truck fairly sparingly, about twice a month, but I'm pretty sure it didn't do this in the past. Any ideas? TIA.

 

Here's another clue to try and help diagnose what going on.

So this intermittent blowing subsided last night as i went out to dinner. All levels, either side of the temperature spectrum, at every vent setting.

However today on my way to work I made an enthusiastic right and while I was at Full Cold WITH A/C, I heard potentially was a *clunk* and the next thing the climate control was blowing full heat, A/C on, but not blowing cold. I tried to think nothing of it, had to go to work.

After work, on my drive home, Fan level 1, Full cold with A/C. No problem, no intermissions in the fan. Any ideas yet?