I recorded this sound (with my iPhone, please excuse the poor quality) on 29 April 2012 near my house in Concord, MA. Have a listen and see what you think. For a little additional background information, which will also give you a hint, read the footnote below. ((This is a fairly common variant of the song of a common bird here in Massachusetts. I suspect that local birders, at least, will identify it easily, but I think it is specific to this area so I’m curious to know if it sounds familiar to birders from other regions.))
Click this link to listen to the sound:
And when you’re ready to know the answer click here.