Distraction? A somewhat paranoid part of him thinks, as he turns back towards the source of this noise.

Or maybe he had imagined that first noise, after all. Harrumph.

"I don't suppose you heard anything, either?" Walter asks, as if to open air.

"I mean, you don't have to answer. It's not like I was expecting company..."

He doesn't sound angry, which may be a good sign?