I am set to do the front axle service this week. This seems like a good time to address any front differential problems. I've had a noticeable (but not loud) whine under load at 50-70 mph for the last 10k miles or so. It really hasn't gotten any louder/worse during that time (more or less a year). The whine appeared AFTER I changed out the front diff oil after I bought the truck--the old stuff was thick with moly (I also changed out the center and rear diff oil, engine and transmission at the time). Finally pulled the front DS and locked the center diff and went for a test drive: the whine is gone. Since the whine hasn't been getting any louder over the last 10k mi/year, is there really any reason to pull the diff and replace the pinion bearings? I can live with the slight noise. I've lived with it for a year now and the truck doesn't seem to be any worse for wear. I couldn't find any play at the pinion flange, but there isn't much, if any, preload. Truck has 180k+.