Video of the sounds: https://www.youtube.com/watch?v=NmstXp9ttAk

I have a Kenmore HE2 Plus Front Loading washing machine. The video shows the sound it makes but it may also be helpful to know I have cleaned out my drain catch, I have removed the rubber hose beneath the drum with the ball, I have removed the top panel and back panel and have crawled inside the drum with a flashlight trying to find the source. The motor is fine, the belt is fine, there is no "play" in the basket. It moves, every once in awhile it will "get stuck", just for second between the grated drum and the plastic one and there is a louder boom before it goes back to rattling around again. If I spin the drum really fast, I can launch the thing in to somewhere and it's quiet for a bit, but shake the whole washer and it is back rolling around. Whatever it is, it moves, like a coin or a metal nut. How do I find this thing and how do I get it out?! Also, the machine can run a complete cycle with this issue and not give any error messages, clothes are clean and all the water drains. I am not running it until I fix it, but just for the knowledge of it, it could.