When I start my car, and while it's still at idle and stationary, I hear a noise which sounds like a fan or belt hitting something, but at a low frequency of 4 Hz. The sound is like rubber or plastic impacting something and is not a chirp or squeal like a belt. After around 20 seconds, it stops on its own.
I've narrowed it down to the "Inside Air" function. When I switch it on to recirculate inside air, it makes the noise for several seconds. It happens every time I switch it off and on again.