Knocking in Rutland County, Vermont

I put together a mountain bike trip with a cousin for a weekend in Central Vermont near the town of Plymouth in the Calvin Coolidge state forest. We decided on a Lean-To shelter called TinkerBrook on the outskirts of the forest near the backside of Killington Peak. One reason for this location was because of the steep topography the area offered for a mountain biker. Also, not to many people visit this shelter according to the Rangers I've talked to before due to the hike in and lack of 4x4 access as well. The place offers nothing more than a view of a steep forested ravine. The shelter is right on the edge of this ravine as well. We travelled up Shrewsbury road which intersects RT100 south of Plymouth and then heads west almost straight up the nearest mountain in a series of switchbacks. We then parked our vehicle on the bend in the road where tinkerbrook shelter trail starts. The trail/road is heavily blocked off by boulders and easy to miss. We packed up the bikes and headed down the old trail/road to the shelter. The shelter is about a 3/4 mile off the forest road we parked the vehicle on. We set up camp for the night in the shelter and did a look around. The place offered no trails to ride on and the ravine was so steep that you needed to climb out of it using the roots of the trees in it. The place was very isolated. We headed off to bed around 9:00pm and left a campfire going near the opening of the shelter. A few hours later (12:00am) my cousin woke me up saying that he was hearing and feeling knocks on the shelter. I told him to go back to sleep. Then I heard and felt the noises myself. The sounds were like something big pushing against the shelter. I thought it could of been a moose or bear and decided to go around back to see. I took a flashlight and went around back within a minute of hearing the noise again. There was nothing there to see. This continued a few more times during the night until maybe 3:00am. I felt the bumping sounds near my side of the shelter on occasion. We didn't get much sleep and at one point I even pulled all the firewood close to the opening to keep a large fire going. In the morning we looked for any damage to the shelter and found nothing. We also looked around for any sign on the ground (footprints, loose rocks, scrapes and hoofmarks) but found nothing. We decided not to stay another night and headed out.