Rana Grylio

We heard a weird sound from the woods, like a pig grunting, but the grunts were evenly spaced and went on and on.

I googled "nature sounds" and found this Smithsonian site where you can purchase CDs, including nature recordings. The page is full of samples to listen to. Sure helps figure out which critter you heard - in this case, an amphibian.

Scroll down to #143, The Grunt-Like Sound Produced by the Pig Frog. That's what is makin' a racket in the woods tonight.