Hey folks. Gotta question. On my 07 fj, ever since I purchased a year ago you can hear slight noise coming from rear differential. My mechanics store says it's the Pinion bearing. I was wanting to drain gear oil and replace w Royal Purple synthetic oil. The mechanic says doing that could actually cause it to fail sooner. I don't see how it could do anything worse to it, if not actually be good for it. I'm not going to touch it untill I hear from you all. Thanks a bunch.