I'm going throught the same bull with mine right now. It seems to have happened after driving through puddles in a gravel yard? Who knew. It was on for the longest time, then periodically off. I tested the ohms for the front 2 and got a acceptable reading, and the rear gave nothing. The rotor sound seems kinda normal, it's not always supposed to be 100% silent but worth a good look anyways. I found one of my sliders scraping the side of my rotor once, not a pleasant sound. I'll find out hopefully today what the prob is and report back, I'm thinking it's the rear sensor on the diff.