The noise? Vampire. Of course. Dawn wondered how she'd explain this one to Mel. Drug addict? Botched plastic surgery victim?
Mel punched it, and Dawn had her knife out already. The stake was a little further out of reach, and she didn't think she wanted to try and actually slay the thing on her own. The best chance she had was to injure it and then outrun it.
"Get back!" she yelled, one arm reaching out to - what? Pull Mel back, or just warn her off. Get her away from the thing, at least.