Humanoid in Snohomish County, Washington

I was hiking, with my dog, at Wallace Falls State Park on 4/26/11. I started the hike at about 11:30am and there were only two other vehicles in the entire parking lot. I had hiked passed the upper portion of the falls, following an old logging road up to Wallace Lake. I only saw one other hiker coming down from the falls lookout. At approximately 2pm, my dog and I were walking towards the lake (it was about 1.5 miles away). We heard a very strange, humanoid yell come from across a marshy bog area. We both were taken by surprise and stopped. I looked across the bog area up towards the thick forest on the other side (about 75 yards away). I couldnt see any clothing of a hiker or potential body of a humanoid creature. The sound however was very interesting. I've spent many hours hiking the Washington state forests. I know what certain animals sound like when calling for a mate or calling to signal a warning. This noise was different. It was comparable to a person yelling directly and loudly "yoouuuuuu!!!". My dog and I stopped dead in our tracks and listened. About a minute went by and I heard the same noise again from the same area. The loud and direct "yooouuuuu!!". It was very strange. I'm positive that whatever made the noise was either a human toying with me, or some humanoid creature warning me of its presence. Being miles up alone in the wilderness, I didn't want to John Wayne across a bog into thick brush to investigate. It was the first time I've ever heard such a unique sound while out in the forest. I will never forget the look of confusion on my dog's face either. I'm sure mine looked the same as well.