Aux water pump - is this supposed to run while driving when HVAC heat

[wrinkledpants]

Was a bit chilly here in Denver yesterday, and turned the heat on. While driving, coolant not fully up to temp yet, I could hear my after run pump running. Mine is loud, and might need replacing, but not sure why it was even on. Coming home last night - same thing. However, with the climate control on "auto," if I moved the temp low enough (about 70 degrees), the pump would shut off. So, it seems that when the HVAC unit is calling for heat, it turns on the after run pump - at least in my case. Go back up a few degrees, and it would come back on. This is with the car running - not when it's shut off. And, this happens whether the car is up to operating temp or not.

Anyone know anything about why this might be happening? I'm not sure if I'm just noticing it because my after run pump is quite loud, or if there is a problem and it shouldn't be running.

Also - anyone else hear their pump? Mine is louder than the air compressor. I could hear it buzzing faintly over the radio and the HVAC fan while driving. I can also feel the front fender vibrating if I shut the car off and it's running as part of the after run system, or with the "rest" function. The aux water pumps I've had in other cars were whisper quiet. You'd have to listen closely after the car shuts off to hear it. The one on this car is clearly audible while driving - almost to the point that I have to turn up the radio.

[wrinkledpants]

Figured it out. Apparently the aux water pump does run with the call for heat, on top of the after run circuit and rest function. Found a TSB that adds some sound deadening material to this pump to isolate it a bit more since it's hard-bolted to the area just in front of the driver's door. Cars after a certain VIN came with this from the factory.

It's TSB 1945. Doesn't show a factory part that you need to add, just cutting foam strips and the places where you need to add them.