Rear heat question for van

I have a 2002 Kia Sedona with 137,000 miles. I purchased the van back in Aug and until now have not had to use the rear heat. When I did turn it on it worked okay but I got what sounded like a squeeling belt sound that you get when your serpentine belt is loose. however I don’t get that sound unless I turn on the rear heat. How does the rear heat in this van work and what might be causing this sound?

There’s probably an auxiliary fan for the rear system that’s not lubricated or has a bad bearing. It squeals when it spins.