Report 15019: Possible vocalizations heard near Yorkville

Around 11:23pm on june 20th 2006 my girlfriend, myself, and the dog stepped outside on the back porch so my girlfriend could smoke and to let the dog out to go to the bathroom. The porch faces a wooded tree line area that runs in the backyard and runs through the whole subdivison.  So we open the sliding glass door to step out and we all step on to the porch the dog was still. Then she ran barking straight to the back fence, that is just in front of the tree line area, my girlfriend tells her to be quiet and to stop barking.  She doesn't, then after 5 minutes she stops and we were on our way in, so to see the dog because we couldn't see her I decide to use the display of my cell phone to see if I could see her, because it is a bright display. I see her coming to it but to joke around with her I start waving it around in circles. Then from the back tree line my girlfriend and I both hear this strange 'coo' sound with breaks in it. I freak out and push my girlfriend aside and run in the house; as we were inside and I locked the door. Then I say did you her that and she was like yes what was that, I though it had to have been a bigfoot...It was like nothing I have ever heard in my life.  [Edited]