Mystery Bog Bird Sounds

I got a call from someone telling me that there was a mystery bird making strange sounds out in the bog across from his home. I heard the strange sounds and did not know what to make of them because I could not find the source of the call. I thought maybe a cuckoo or a marsh bird of some sort. I even fell into the water trying to track this mystery bird down. After falling into the water and failing to match up the sound on google, I decided to ask for help. 
  
There was a birder who lived nearby who is a step up from me in the birding skills department that offered to help (thanks Tim). The mystery bird happened to be a Pied-billed Grebe which I have seen many times but never heard. They sound a lot more interesting than they look! I never did see the grebe this time as it turned out to be a very sneaky one. You can click on this All About Birds Link and listen to some of the sounds I was hearing from the Pied-Billed Grebe

Have you ever come across a bird vocalization that you couldn't identify?