Alright guys I figured that it time for this thread. I bought my runner about 2 years ago, and ever since I've had it it made a loud banging sound but only in reverse it has'nt gone out but I'm getting a little nervous about it now. I checked drive shafts and all the basics but it sounds like the trans. thanks

 

Check your pinion nut.
When I got my 4runner it was making noises in reverse and it turned out to be the rear pinion has loosened up and was contacting the diff carrier.

 

u-joints too.