I actually had this very problem with a Ford rental car. It had "Microsoft Sync" for its infotaiment system and it suddenly started to output very loud white noise over the audio system while I was on a freeway. And it wasn't responding to volume controls.
However, simply stopping the car and turning it off didn't help. I had to go online, find the location of fusebox, and pull the fuse to hard-reset the infotaiment system.