Q: Rear differential noise.

Sounds like you need to take it back to the shop where you had it changed. First you want to be sure it has enough of the correct oil. If it turns out it is properly filled, it may be necessary to open it up and have another look. Differentials are a tricky business. There are a number of dimensions in there that need to be carefully set up when the differential is built or you will get unwanted noises and it will wear out more quickly. If you need a second opinion you can contact Your Mechanic. They can send a technician to your home or office to check out your Noisy Diff and let you know what kind of problem it has.