Binny

This is my first post and I am hopeful it will go thru because I really need some advice on the rear axles and CV joint replacement for my '98 Legacy 4dr sedan AWD auto car that I am trying to keep on the road. It seems to have an annoying vibration in the rear that sounds exactly like the old Chevy universal joint noise when they go bad. Hope you folks won't make fun of my ignorance but my head is spinning from all the options out there for rear axles. How will I be able to tell wich one is gone, will there be obvious play and could it be a wheel bearing? Biggest question is though is there a difference between the rr and left rear axels? Is there a difference between the standard and automatic transmission? And when I do replace one should I buy new circle clips? Binny