This is the one and only episode that J.Q. Quintel of Regular Show fame storyboarded alongside Kim Roberson.
Two things, both related to drum cymbals.
First, there's a layering error when Ferb plays the rimshot, you can see the outline of his hand even though the cymbal should be obscuring it.
Second, The drumset in this shot during the E.V.I.L. B.O.Y.S. segment is... interesting. I don't think I've ever seen a drumset with only three toms and three hi-hats.