Bird distress call

I heard this bird sound in the back yard - it just seemed to go on and on. I couldn't see anything or describe the sound to Google, which sometimes helps me identify species (I nailed down Swainson's thrush the other day, after about a century of wondering what it was). Sounded like pew, pew, pew, pew, pew, pew, pew. . . It was hard to say if the bird was in distress, proclaiming its territory or trying to attract a mate. This video includes perhaps the worst camera work I've ever done, but the audio is very interesting. The sounds accelerate as time goes on until it's a kind of machine-gun bird sound.