whenever i switch the air vents from front defrost to like the leg area it makes a thud behind the dash like its gettin stuck on something for a second and then popping. the air then comes out the bottom like normal...vice versa. Any ideas on what could be doin this??

 

Mine does the same thing. It's been like for as long as i can remeber

 

mine just started a month ago so i was hoping someone has ever had this happen and fixed it, but you sound like your "popping" isn't hurting anything so i guess i won't worry about it.

 

It's the vent closing all the way. Mine used to do that until I detached the heat vent from the back of the unit, but if I reach back there and pull the cables with my hand, it'll still thud.
Dunno if it's good or bad, but that's what it is