Heater Knocking

It's kind of hard to describe whats going on but bottom line is when I turn the heat on there is a very distinct knocking sound coming from behind the glove box. I haven't had much time to research where exactly it is coming from but somewhere around the fan behind the glove box.

It only starts knocking when I turn the heat past about the 4th red bar on the dial.

Anybody have any clue what this might be?

 

Yep, I had that happen... was a pile of acorns from the damn chipmunks. Only made noise when it was 4 or higher, just like you.

 

man, i drive my truck daily so not sure how that can happen. But it has been getting colder at night so that may have something to do with it. How did you get it out? I'm assuming it comes from the engine side somehow?

 

This "knocking" could be the mixing plenum door servo.

Read this: http://www.tacomaworld.com/forum/2nd-gen-tacomas/229312-blend-door-servo-malfunction.html