High pitch/squealing noise ust started when I turned on my heater.

SOURCE: squealing NOISE possibly from fan belt

There are several things you should know;

1. Power steering belt, when you make a turn, sometimes make noise, because your car needs power steering oil,=transmission oil.

2. when you turn on AC then you can hear a loud noise, you must check AC compasser,If the head wheel frozen, it will make a lot noise, that you have to fix your AC compasser.

3.check these two first, if both ok. shot some wd40 or lubricate see if it's work.

Hope this can help you

SOURCE: squealing NOISE possibly from fan belt

Belts stretch from new. Try to tighten them again. Hopefully the are not glazed or this may stay with you.

SOURCE: Squealing noise in 2002 Nissan Sentra

Seems like a drive belt problem, to confirm pour some water on belts the noise should go away or may get louder for a second. If either happens the belt or belts needs to be adjusted or replaced. Good Luck, If I fixed ya, leave me a FIX-YA comment thanks