While on your way out of the room, you hear a voice from outside. "We know you're in there, Karg!" It says. "We've got the place surrounded and we've brought a cannoneer. So don't try anything funny. Now come out peacefully and nobody gets hurt."
Those of you who have been in the neighborhood of Galgenbeck for a while know that a cannoneer is a large golem type creature that is mostly used for siege battles. That would explain the noises you've been hearing. It's great at breaking down fortified walls and will make short work of a tavern like this.
One of Karg's men speaks up, saying "Karg, this is my uncle's tavern. Maybe we should just leave if they have a cannoneer." He promptly gets knocked out by another companion and added to the barricade pile while Karg scoffs. You can tell from his face he's not about to give up.