Alright guys, so I apologize for the late response. I have gone under the car, checked for rattling heat shields, checked to see if the linkage is rubbing anywhere, i've torn the center console out, checked all of the bolts, tightened the connection where the fork meets the shifter. I literally cannot figure this out. I even removed the bracket that held the downpipe to the transmission, since it had broken when I did my up-pipe install.
I've included 2 videos here, first is the car decelerating in 2nd gear, the rattle tends to happen around 3500-4000 RPM REGARDLESS of which gear i'm in, which is what makes me wonder if it's just something making contact with something else; sound tone changes when I move the gear selector in gear.
The next video is a quick shot of the car at a stop light in 4th gear with the clutch depressed; the rattle is still present when revving the engine with the clutch depressed. Again, I have tightened everything I can think of; I really don't know where to begin here.