Well i had the coolant flushed at the local GM dealer, because it was 0 degrees outside, and i wasnt planning on freezing. They flushed it out and found that the heater core was somewhat plugged so that would explain the really poor heat i had. But now when im drving anywhere from 1000 to about 4000 rpm, i get this noise coming from what sounds like the dash of almost a small burnout sound or a belt squeal.

What could it be? And i havent lost any coolant, all the fluids are good.
And i have a brand new main belt, A/C belt, and both idler pullies have been replaced about a year ago.

I also have a horrible almost metal on metal sound when its cold out that goes away after a minute or so? Alternator?

Could they have damaged something when they flushed it?

thanks for the help guys