I have somthing that is driving me NUTS!!!!!! I have this little knocking sound that is coming from right underneath the gear shift area. It's almost like a vibration kind of knock and it does it whether the car is in park or when I am driving down the road. I changed the tranny mount for the 2nd time in the past 6 months yesterday and i don't know if this means anything or not but when you put the crossmember back over the tranny mount and bolt it up i had to fight with that thing like crazy to get it on. It seems the first time I changed it it lined right up with no trouble but this time it seems as though i had to start the 2 bolts on each end of the crossmember and tighten them just a little and than really put pressure on the main tranny bolt in the middle to get it to go on as it was tighther than I remember it last time.????? Anyways i don't know if that means anything but i thought it might be somthing mechanical but when the car is in park it still does it. I don't know but while in park is there anything mechanical actually moving in this area? When i turn the car off it will have a little vibration as the motor kills off? I did run out of my frineds driveway a while back and somthing underneath the car scraped pretty good because it was a steep driveway. does it sound like maybe i bent somthing like the exhaust and it's rubbing or does it sound like there could be somthing mechanical going south down there. I have searched for it and it appears to be originating right underneath the gear shift selector. any help on this would be greatly appreciated as I don't know where to start? Thanks guys!

 

I forgot to mention the car is a 94Z with an auto trans. it just turned over 129,000 miles.

 

Check to see if the piece of metal thats back by your drive shaft (I don't remember what its called but its not the trans crossmember) isn't slightly bent.
I hit a peice of tire on the interstate one time and it bent mine up far enough that it would bump the exhaust and made a noise.
It was really annoying.

Edit: The above overly described part is called a Tunnel brace.

 

If it's hitting the floorboard, Check for rub spots on the floorboard

 

My guess is internal catalytic converter noise. With engine cold and converter cold, get under car and tap on converter with palm of hand and see if you can produce the noise.

 

I know exactly what you mean!!! I just did a cat-back two weeks ago and the same thing is happening. I checked for exhaust clearance and there is at least 1/4 inch buffer from touching anything. But I hear it on the highway at cruise or sitting at idle. I checked the driveshaft loop but it is fine and not rubbing.

I've got an M6 and it is making noise right in the rear tailcone before the driveshaft.