Gears & Axles - banging problem need advice

as soon as i put the car in gear and start to move forward their is a loud thunk and gets faster as the car speeds up, at first i thought it was my rubber tranny mount cuse it was torn apart so i replaced it and the problem still remains, its not the exhaust because i am running it open headers because i thought the exhaust was banging, so its not my tranny mount and its not the exhaust im thinking it may be my drive shaft, or worst case broken rear... any help would be great.

just alittle about the car its a 98 with 79k miles 6speed lt headers and a torquer 2 with all supporting mods. it made 380 at the wheels still has stock 10 bolt and stock drive shaft, spec stage 2 clutch

this happened in my other car i replaced the u-joint cause that was shot pulled out in the road and it did it again it was that the pinion cap bolts weren't tightened down and it was slipping on the gears, pull the diff cover before you keep trying other stuff my ws6 now is making alot of noise and i pulled the cover and nothing is noticably wrong

http://www.exoticperformanceplus.com/services.php?service=58

Look for the problem shown above which I have seen several times. Bob

just to update this, the problem was 2 complete teeth were sheered off my gears and a few more were chipped. got a 12 bolt installed and problem solved