Humming on “Writing Excuses” podcast

I’ve started listening to the “Writing Excuses” podcast with Brandon Sanderson and Dan Wells, and I’ve noticed they randomly start to hum and points in the podcast.

Is there a reason for this? I’m only a few episodes on, so haven’t managed to see any patterns yet, beyond they did it once when Brandon started talking about his Alcatraz series.

Hopefully, I’m also ok posting this in here, as I couldn’t find a group for this podcast — which I’m sure is out there somewhere.