I am traveling with my 2003 Suburban 1500 5.3. I started noticing a whirring noise coming from the rear end while under load above 45 mph. Noise goes away on deceleration and low speed only audible while under load and consistent with wheel speed, not rpm. Sounds like pinion gear type issue. I am towing about 6k lbs and have done a lot of mountain towing this trip. There is moisture on the pinion seal area, but no evidence of dripping ar anything major yet. Is this anything to be majorly concerned about yet? I have 1800 miles more to get home. Anything else I can look for in a parking lot to diagnose further? Thinking to check and top off fluid. Is this doable in a parking lot without a jack. Any other advice?