Mike McCready of Seattle based Pearl Jam gets credits as "special guest composer"
and the song Peter is listening to at the end of the episode is "Is there a ghost" by "Band of Horses", also Seattle based.
Musically the one non-Seattle reference I noticed was to Leonard Cohen. The slogan on the pen "Find the crack" and the addendum "that's where the light gets in" references Leonard Cohen's "Anthem"
There is a crack in everything
That's how the light gets in.
Thankyou, I was just about to post and ask what the name of the song was that Peter was listening to