What could this growling noise be?

A few years back, I was still in high school, a friend was spending the night at my house. We were still 16 or 17 and decided to sneak into the entrance of the woods behind my house around 1 or 2 am to smoke a cigarette since we weren't allowed to smoke. I remember it was really snowy and there was about a foot of snow already on the ground, and we were just about finished smoking when we heard this awful loud growl/roar/bellow it of course scared the living hell out of us and we ran inside. Serves us right I guess, but I'm 21 years old now and it still bothers me because no one can tell me what they think it is, I live in southern PA and the closest thing that sounds similar is a bear, but I know they don't live here, and I'm pretty sure they hibernate during the winter, and it wasn't quite as deep as a bear, I've heard that buck can growl as well, but I know the way they sound when they grunt and it didn't sound like that either. It almost sounded demonic, but I would sure love to know because it still bugs me.