BAD noises :-)
Seriously, the ten stock bolts have a tendency to back themselves out. If you are very lucky, when they back out enough to hit the inside of the case, they may just snap off and fall to the bottom of the case. One PCNC member actually fished out all ten bolt heads, and several pieces of bolt threads, after one fell out when he pulled the drain plug to change gear oil! He said the shifting was fine and there was no noise. OR the snapped off head can wedge in the gears, lock the tranny, and shatter the case and who knows what else. I infer you have a noise? Maybe a bolt has backed out just enough to hit on rotation but not get fully whacked and snapped off? I suggest you find a 17mm hex head socket (Used for VW drain plugs and often found at Kragen or such) or allen wrench, remove the drain plug on the bottom and see what you can find. Use a bent wire to fish around for pieces. Do this before driving the car again. You could be right on the verge of a major problem. That ZF is the most expensive piece of the car when it comes to replacement. Keep us posted.
Larry