Windshield sounds like Popcorn in Cold

This is our third winter with a gen 6 Outback (2 different cars) and have no noises anything like what you’re experiencing. That’s not normal as the dealer is telling you. Noises of that type, in that frequency range are highly reflective, and windshield make great reflectors. The higher the pitch of a sound, the more reflective it will be. I’m not at all suggesting it’s not the glass itself, just that it would be easy for something in the dash/cowl area to seem very much like it’s originating from the windshield.

Next cold day when it’s making that noise, do some experimenting. In a safe place, and with an assistant, try placing some sound deadening material in various places on and around the dash area while you drive, see if it changes your perception of the sound source. A fluffy, bulky towel (dark to avoid visual reflections for safety) will work fine for this. Also have your passenger put pressure against the windshield and/or dash with their hands in various places to see if that affects the noise. Try anything you can think of that might alter the sound in any way. If any of this yields potential clues, make a video to show the dealer.