Hey buddy,
I've got a 4AC powered AE82 and I experience the same problems.
I've figured out though that it depends on my revs and how I accelerate.
For example, if I let the gear rev higher than usual and then change the likelyhood of this happening is alot less.
It also seems to happen when I change at lowish revs (around 2,500) and then push the accelerator all the way in (floor it).
However if I put my foot on the accelerator and gradually increase the throttle (like I'm supposed to) then I don't have the problem anymore.
Normally it's okay but when you're turning onto a main road I need to floor it because the 4ac isn't exactly the best engine around and it's frustrating to hear the rattling noise.
I sort of lose power though. While it rattles it seems to be that the car is maintaining it's speed but revving more. That's what I mean by sort of. I'm not losing power (slowing down) but I'm not moving any faster either, it's just revving more.
Try changing at higher revs and after changing try and gradually push down the accelerator and see if it's any different.
My knowledge of cars is very limited, hope that helped in any way.