Year old pit mix loves her crate and is not at all destructive if left alone and un-crated, but howls nonstop. Help?

Our year old pit mix is a total sweetheart. She's a cuddly bundle of energy, but gets plenty of exercise daily. I have a hard time believe that is the issue here because when I'm home she's generally a couch potato after long walks or trips to the park.

It seems like no matter what I do, she whines when we leave her. It doesn't matter if she has a puzzle toy or if she's just been at the park for an hour. She howls almost nonstop. I started thinking maybe she hates her crate (though that seems unlikely, because she voluntarily sleeps/naps in there and hardly ever protests going in), so I started leaving her uncrated. I don't think its genuine separation anxiety, because she doesn't chew/destroy anything, or soil herself. She just lays by the door and whines. I'm at a loss as to what to do, and it's starting to be an issue with my housemates. Help?