Standing/sniffing at door CONSTANTLY??

So my 8 year old GSD has some new weird obsession with my front door. Previously, she trained herself that it's some sort of wall that she can't go through(she always leaves through the back door, not front). But for the past week or so, she's been sniffing at it when it's closed and today when we was carrying in groceries, she started to growl(like seriously growl. Not like a play growl, never seen her freaked out like this). Nothing's happened that we've seen. It's never bumped or hit her or any of us. It didn't make a loud noise or anything new. Just the same old door we've had her entire life. She got a clean bill of health at her vet appointment a month ago

Any ideas because we are stumped 😭