how can i fix this. this only happens in reverse,drive,2 and low and if i accelerate the sound of the rattle dies down a little.

Even an expert tranny mechanic will need special tools and equiment to do tranny tests and I hate to get into a try-it guessing game. Take your vehicle to a good tranny shop and they should be able to tell you what's wrong and how much it will cost to repair.

I read elsewhere:
"Also, the infamous SAD (Auxilary Drive) problem that make the car vibrate during idling at the stop lights. Toyota has a fix kit that cost $200 instead of replacing the whole thing for $1200."

It sounds like this may be your problem. I beleive I have the same problem, I have an appointment this week to get it diagnosed.

I had similar problem, my cat converter had loose pieces bouncing.