Engine knock? (with video)

[1988 4.0 mj] Recently I have had a nasty sound coming from what seems to be under my distributor. It sounds like there is a loose nut rattling around. It is consistent with rpms, and the sound is there 90% of the time. The distributor is only a year old, I pulled it out and checked the teeth on it and in the block, they looked fine. The motor has somewhere between 275,000 and 300, with no rebuild that i know of. There is also a small dent in my oil pan in that same area from my upper control arm hitting it, could this be interfering with something? I am going to pull the pan to see if I can visually see anything, but any advice would be appreciated. thanks...