2002 Chevrolet Silverado Z71 4x4. Okay, on my road trip earlier this week I noticed sort of a light "roaring" sound that seemed to be coming from the front end of my truck. It seemed most noticeable between 40 and 50 mph. It sort of sounds like a bearing or possibly the 4 wheel drive not completely disengaging. I stopped in a parking lot, pushed the 4 HI button and wait for it to engage. As I proceed to drive it, it appears to not be locking the front axle in place, but then when I turn left or right, the rear wheels begin locking up. I can push the 2 HI button and it seems to be disengaged but I still hear the light roaring sound from the front end while driving (sort of the sound that it normally makes when the 4x4 is turned on). I also noticed a drop in my fuel mileage on the trip (about 3 mpg lower than normal) so that made me think it wasn't totally disengaging as well. Any thoughts?

might be the front actuator going out. I believe it is like a $200 part. Not sure though.

sounds a whole like what mine did just before the transfer case exploded on LBJ in 5:00 traffic!!!!!!!!

The rear wheels aren't affected by putting the truck in 4wheel drive bc they r the main drive tires. It sounds as if an actuator in the T case isn't fully disengaging. Fix it soon or spend lots of $$$ when it breaks, it can damage a lot of parts. It has happened rogue past 2 trucks I have owned, chevy and ford. The chevy happened under a load trying to get a cattle trailer moving, the T case didn't disengage, it popped shuddered and broke. The ford's "shift on the fly" failed to properly engage while slow rolling it and disentegrated the gears. Also on your truck, the front tires are always spinning the axle which is always spinning the drive shaft, the noise comming into play at the 40-50 mph also males me think it the T case bc u r then exceeding it's limits while in 4wheel drive. Replace the actuators, it's easy