Screaming or howling in Snohomish County, Washington

In the summer of 2000 I had two strange encounters with a creature I will simply describe as a monster by the way it sounded. on a warm summer day at dusk I stood with my two dogs at the edge of a ravine that had a small stream that emptied out of a small pond at the edge of my property. The back 10 acres was heavily forested with thick underbrush. I could hear something very large moving through the thick underbrush and downed alder trees. Large branches were breaking like twigs. While the sounds of the trees being snapped were happening loud roars and screams like I have never heard before or since were being vocalized. I yelled. There was no response, just the same noises happening. I did not want to walk into the swamp at that point. I listened for about 10-15 minutes. The two dogs I owned that were very brave watch dogs just stood by my side, not wanting to investigate. This was odd in itself as they were very territorial. I remember them looking up at me with a look like "were not going in there". I went inside the house and told my girlfriend as I wanted her to come out and listen. She said if it was what I said it was she didn't want to go outside. We stayed in the house the rest of the night and I was not scared but very tingly on my skin and alert. The next day i walked into the swamp to try to see evidence of the creature. I didn't make it very far because of the mud up to my knees and thick russian thistles. My friend came over later that day around dusk. I told him of the encounter and he asked where it had happened. I walked him to the location. When we arrived the same thing happened as the day before. The creature was still there and I was just down in the swamp a few hours earlier and heard nothing. My friend listened for about five minutes. I asked him what he thought it was. he replied,"I don't know Chuck-but good luck". Then he hurried to his car and jumped in and left just leaving me standing there with this thing roaring. I went inside the house with it still there. I didn't feel like shooting it. It didn't pound on the house or anything like that. I never heard it again after that. I sold the 20 acres and the two houses within 6 months after the incident. Good luck to the new owners.