I appreciate everyone's help but so far no dice. None of the birds makes the same sound like what I'm hearing. Actually, since the vowel sounds are all I have to go on, rather than saying it sounds like cheeseburger, I should say it sounds like a long e sound, drawn out, followed by two short "er" sounds. Like: eeeeeeeee ur ur. Emphasis on the eeeeeeeee. The whole pattern is repeated, so altogether it's "eeeeeeeeeeee ur ur, eeeeeeeee ur ur". Maybe that will help.