Knocking in Snohomish County, Washington

Me and my friend are rock climbers. We've rock climbed nearly everywhere in Washington state. The Pacific Northwest is the main area we've climbed in, and the area we know the best. He is a hardcore skeptic. I on the other hand am a firm believer. I've done tons of research through books and documentaries and consider myself to be fairly knowledgeable about the subject. After this experience my friend is now been having some second thoughts. It all started in the early morning... We drove up to the trail head about 5 miles on a gravel trail to the trail head. We got out of the car and put on our packs, locked the car and started to head up hill. Ours was the only car in the small parking lot. While filling out the trail registry that's when I heard the first knock up hill about 30 yards away. Like two minutes later another knock was heard down the hill and past the road, about 50 yards off. Every now and again you could hear sticks breaking like something was stepping on them. The sound of one stick breaking was heard then silence. I tried to do my own knock and that was responded too after about 30 seconds. That's when we started filming. After the film we decided to move uphill to go and climb. My friend still wasn't really buying it. He thought they were just sticks falling off of the trees. After walking about 17 feet up the trail we heard another knock in the same place. By this time my friend was asking me if they're ever hostile. I was thinking about it being intimidation but I didn't think that's what they were getting at. After walking about 30 more feet up the trail we heard the sound of a rock tapping on a tree, in a very repetitious pattern. For my friend this was the point were he was staring to take things seriously, and wanted to leave. I had no rejections. Before leaving I tried looking down the hill (where the other knocks where coming from) to see anything. The terrain didn't drop off like expected. The road was only three or so feet higher. The woods where very dense. Anything could hide in them. A few days later we went back up to the same place to actually climb, only to be shut down by the rain. We still decided to do the hike up to the base of the climb anyway. After a little while I thought to make a knock as well as some whoops to see if there was anything in the area. I had no response. About half way up we saw a standard stick structure. As well as a whole lot of tracks going up the trail. We were the only ones on this mountain by this point. And by the looks of it the creatures followed the same trail all the way up the mountain. Until the part where the trail goes out into an open boulder filed.