It's BottleRock weekend up in Napa, and even though the Foo Fighters won't hit the main stage until Sunday, when they're headlining, they took to a small stage last night at the Blue Note club in downtown Napa for a surprise show that delighted all who got to see it — about 200 people or less. Frontman Dave Grohl can be heard in the clip above playing and singing the opening bars of Tom Petty and the Heartbreakers' "Breakdown," covering Petty the night before Petty himself will be headlining BottleRock (which is tonight).

Below, a few more bits of social media evidence.