I have a 2012 Grand Cherokee Overland with ~75,000 miles. It has been used 3 summer seasons to tow our 26′ Travel Trailer throughout the SouthWest, PacWest and the Rockies. The vehicle runs awesome, shifts flawlessly, and in every other way acts fine. But I’ve noticed that when running at 75mph, as soon as I add a touch of gas, or the ACC (adaptive cruise control) does so automatically, I hear a “turbine-like” whine from the rear undercarriage. The rear passengers can definitely hear it the most however. As soon as the pressure is off the gas, it goes away. It’s not super annoying or anything (actually for a while it sounded cool), but I’m wondering if something is about to go wrong? I have always kept up with changing the transfer case, differential(s), trans fluids after each TT tow trip season-end. And upon each visual inspection the mechanic stated everything looked fine or that the fluid change wasn’t even necessary (although it was changed anyway). So what do you think of an occasional whine only at 75mph (or similiar high speeds) that comes and goes based on further acceleration, but disappears once it’s just having to maintain speed? (Like if on cruise control you would not hear it until climbing or recovering top speed after someone slow in front of you moves over and the ACC kicks back in to get up to the set speed). Any thoughts?

 

Just a guess, mind you, but it could be the ring and pinion gear lash is getting a little large. I wouldn't worry about it until it gets louder and starts to happen on deceleration as well. My 2000 WJ is starting to whine at high speed, but it's got 190K miles on it.