2005 Chevy Malibu Rough start

Transmission problem
2005 Chevy Malibu V6 Two Wheel Drive Automatic 120000 miles

When I am starting up my Chevy Malibu Maxx in the morning, I heard a grinding noise coming from under the hood. I've realized it's when I turn on my defroster on the car. I've taken it in and the mechanics couldn't get it to make that sound and they found nothing else wrong. This morning I started the car again and there was definitely a loud grinding sound when the heater was turned on!