So in case anybody is interested, I think I found out what was causing the bumping/rattling. JayhawkJeep had it right....The drivers side coil must have come out of the little grove that it seats into when I was flexing on something. It had twisted about 2-3 inches past the "seat grove" and was just butting up against other side of the plate that the coil sits on. I could see that the end of the coil had taken several big gouges out of the coil plate, so that must have been the bumping/knocking noise I was hearing.

So I simply popped the tire off, drooped the axle, and spun the coil back around to where it should be seated. I took it out on the highway and got it up to a high speed and I didn't hear or feel the knock/rattle.

Thanks for your help guys!

 

When you throw out 100 guesses it is good to hear something stuck

 

I agree, almost makes me wanna recheck my suspension