So I've searched the forums and I'm pretty sure my problem is the Blend Door Actuator....HOWEVER, I see some people saying that there is multiple, one that controls the feet, defrost etc. How do I know which one I need to replace? When I turn the car on there a knock in the dash that's pretty loud, it goes in about intervals of three and does so about 4 times (basically like 7 seconds) and then stops.

On a side note, I've been looking for an answer to another question and wasn't sure if I should post a separate thread or try to get an answer here. Sometimes my car grinds when I shift it into sixth, only sixth. It seems like if the car is warmed up it doesn't do it....only if the engine was recently started or the RPMs aren't I guess "high enough"? Driving to work I hit a long straight away and I typically just drive calm to keep gas mileage to the best I can get and I try shifting around 2.2-2.5k RPMS (leads to about 50 MPH and then I shift into sixth) and it grinds sometimes. But when I drive the interstate to class and shift into sixth at 60-65 it doesn't.