There used to be a thread somewhere that discussed checking and tightening your pieces under the vehicle. Especially with an old jeep, I try to do this quite often. Been getting a bit of a knocking sound, so checked everything I could. On the way home from my last trail run a couple weekends ago, the knocking got much louder. Time to really dig into it - think I found it....
couple missing bolts near the top of the bellhousing that go into the block. Took some hassle (and hour plus) to get the transmission cover pan out to access from through the floor (standard jeep procedure)... Never tried to check those before. Might have to become a yearly check when I do the brake fluid (requires partial removal of the transmission cover pan). Some of the other bolts look to be missing lock washers, so that might help to get those.
Anyway...if you drive old vehicles with lots of mechanical pieces bolted together....check and tighten your stuff...