Bird that sounds like a kids toy/cartoon noise


I keep hearing this strange bird call, like that kids toy where you turn the tube around and the ball slides down and makes a weird downward wobbly whistle noise. Kind of like a cartoon sound when something is falling.

Ive heard it several places and I just don't know what it is or how to describe it any better and I never get an audio clip in time! 

Any ideas based of my very imaginative description of what this could be? Thanks!