Knocking in Prince George's County, Maryland

I was camping on the largest of the river islands on the ******** River in the extra restricted area of the ****'s Central Tract. It is an old growth forest. The understory was mostly clear of bushes and brush. I would from time to time camp out overnight there. I always camp with nothing more then a sleeping bag on the ground. While on the refuge I would not light fires, not cook food, not play music; just pure silence, meditation and observation. Late on this one evening in late July, I heard wood knocking or clapping in the distance from the south portion of the river. I instantly thought of Bigfoot (I must be honest, especially after all the activity I had observed throughout the months prior). I had a large stick with me, so I slapped it against an old tree. At first I heard no reply. I repeated the banging once every few minutes until I did got a response of knocking back. This was in the same location as before. It then returned to silence until about 15 minutes later when another knocking occurred. About an hour after the wood knocking I heard definite bi-pedal footsteps walking very slowly. The footsteps were obviously coming from something which was being very cautious. The creature was approaching from the south where the wood knocking sounds were coming from. I assumed that it was on the next island downstream (which is separated by a narrow deep channel of water 15 ft across by 6-10 ft deep). I remained silent the whole time as to not scare it off. The next thing I heard was a loud "kerplunk" of something falling or dropping into the water channel. Around 15 minutes later I heard a few faint footsteps walking away back to the south (these steps were not as gentle or cautious as before). It sounded as if it were tired of the game or just leaving because it investigated what I was doing. The rest of the night was silent. Following morning: The next morning I went over to the next island at the break of dawn. I found no obvious footprints or evidence. However, I did find possible large prints but they were not overly revealing.