Question: Is it, when you turn on the heater fan, or the heater itself. Heater fan squeal when cold is not uncommon, and something which happens with most cars, had that with every single one of them so far. If really the fan, do nothing, until it won't go away any more.
Normal course of action: Replace fan assembly. McGyvering: Remove and disassemble (not straight-forward, mind you), clean and polish off the rust from the shaft, and re-grease it, then reassemble -may need some good glue - reinstall. I've done that in the past on my old Toyota, it ran without any noises for another 4 or 5 years until the car was scrapped.