My heater seems intermittent. It's hard to describe, hence my inability to Google for it. When the car is on, engine not started, the blower motor will move at full speed, and when the car is on, engine running, the blower motor slows down drastically. I also have an issue with the heater intermittently running. When I drive, there's a strange sound occurring around 2500~3500 rpm, like a rapid blow off of pressure coming from somewhere under my passenger side. I can't quite figure out where to start looking because it only happens when driving, and when this sound occurs, the cabin temperature drops. This only happens when the heater is on, when I switch to AC, the sound disappears.
Could anyone point me in the right direction? Are these two issues stemmed from the same source?