When I turn the key on I get a knocking, banging noise coming from behind the radio. I also hear something that sounds like a fan. It's down in the area of the heater assembly, not the blower. When I had the heater core out, I don't remember any fan in there. Also, when the car is running the knock doesn't get faster, slower, louder, or softer with any RPM change. Not sure if it's causing any damage to anything but it is really annoying. I'm gonna take it apart this weekend to look but just wondering, any ideas? TIA

 

This morning when I turned it on it didn't make any noise. But this afternoon it started again. I'm thinking, what ever it is, it has to do with temperature inside the car. It was 60 in the morning and 85 afternoon. (At least100 inside) I pulled the carpet back on the console, passenger side, and I can feel thumping on the ductwork which goes to the rear ducts. Still gonna pull the console out (again) tomorrow to see.

 

I just looked at it and found out it's one of the servo motors on the bottom of the heater assembly. Feels like it's skipping a gear, it jumps up and down and the vibration is echoing through the ducts making it louder. Holy crap, I hope I can figure out how to unhook it w/o taking the whole dash out again. I might have to just break it off somehow.