Tonight while driving my 2003 Kia Sedona with the defroster on, suddenly I heard this very loud rumbling which sounded like it was coming from the engine compartment on the passenger side. My first thought was my exhaust had broken, but as soon as I turned off the heat blower to listen, the sound went away.
I also smelled something burning... not quite electrical, maybe rubber.
I pulled over and checked under the hood, and saw nothing obvious. No fluids leaking, reservoirs were where they should be, oil was fine, belts looked in place.
I proceeded to drive home. Once I got home, while idling in the parking lot, I turned on the heat, immediately heard the noise, and turned it back off again. In addition, my dash lights and what not dimmed a bit, as if something was pulling on the engine pretty hard.
What might the problem be? Is there a bearing in something that might have failed?
I don't know if it matters or not, but I was driving through a light rain around 40 MPH when I first noticed the problem.
EDIT: I discovered this morning that this only happens when the defroster is on. With just the heat on, it works fine and there is no problem.