I have a 2004 F-150 SuperCrew Lariat 4X4 with 216K miles. It has been a wonderful truck for almost 15 years now with very little spent outside of routine maintenance. Camshaft phasers, plugs and throttle body were the biggest expenses. I recently noticed a whine or pitched noise (kind of reminds me of the rear end noise you hear on 18 wheelers at the rear of the tractor. If it's below 80 degrees you don't hear it. Outside temps in the 80s and 90s, you hear it and it's very noticeable when I open the rear slider. I recently had the rear end fluid changed out. That didn't make a difference. I can drive 25 miles to work in the mornings with the outside temps around 78 degrees. All quiet. As soon as I leave work and get over 30-40mph, the whine is back with a steady roar. It does go up and down in pitch with speed. New tires recently put on, but it's no the tires. Leaving work the outside temps are in the 90s.
Before I take the truck in and let the dealer do guided discovery, I thought I would ask here for input on the possible cause areas to look at. Thanks!
Lake Park, GA