Well pulled the DS off today and the pinion nut is still where I left it last February when I did the 4 speed swap. Nothing loose, it all looks good. But I replaced all the lock washers on both of my drive shafts. They were original and after comparing them to new washers they were pretty flat. Didn't notice that when I did the 4 speed swap but maybe that was all they had left. I am leaning towards the idea the DS was loose and started to have just enough flex in the system to create that noise. But I'll keep a close watch on it all and double check things in a while.
desmogged 2f, 4 speed