Passing By — Beach Boys

note: This song has lyrics: "While walking down the avenue I stopped to have a look at you And then I saw/You're just passing by"

but Brian decided not to use them. I don't know if these lyrics were ever recorded. You can sing these lyrics to the part Brian is humming.

source: http://www.cabinessence.com/brian/tracks/files/p/passing_by.shtml