yes, it is the differential fluid. Use the guide posted in the forums, I had the same problem around 45k or 50k miles and I changed it and it immediately fixed it. If you listen closely to the sound when turning, it is actually coming from the back where the differential is.
Tips: make sure you run the hose you use to fill the fluid before draining it. Also before removing the drain plug, remove the fill plug to make sure it doesn't need to be replaced. Buy the seals that go along with it, one of mine fell apart after I got the first bolt off, luckily I had decided to change it anyway.