Toyota Tacoma trans noise?

I have a 1997 toyota tacoma with 2wd and a little more than 220,000 miles. A couple of weeks ago I started to hear a noise when I would drive in reverse. The noise sounds like metal scratching and squeaking together. This noise would gradually go faster when the truck started gaining speed. About a week ago I started hearing this noise in drive also. I put the rear up on jacks and used some stethiscopes to see if I could her where the noise was coming from. It sounded like it was coming from the tail housing, so I thought it might be the rear trans yoke that connects to the driveshaft but I'm not sure. What could be causing this noise and what needs to be done to fix it?