Been using my heater a lot lately...over the last month or so, I've been getting a progressively louder noise that sounds like it's under the dash...a kind of grinding squeak. When I turn the heater off, the noise repeats itself, adding a "thump" at the end of it.

I typically use the heater in floor mode (on really bad frosty mornings, I'll run it in Floor/Def to help clear the windshield). The last time I heard a noise like this, on any piece of machinery, it meant there was a bellcrank/actuating rod that was binding up. Does that sound about right for anybody?

How does the HVAC system work in this car?