Chevrolet Repair: Blazer acts like it going into 4wd without button pushed, pinion and ring gear, axle shaft

Question
I have a 98 chevy s-10 blazer that every morning it will make a winding/grinding/wizzing noise out of the front end that sounds like gears are turning that shouldn't be. I can push the four wheel drive button and it goes in and the noise leaves. I can then go back to 2wd and noise will be gone for rest of the drive but after sitting five or six hours it happens again. I'm thinking something that should only be turning in 4wd is connecting after sitting for a while. Thanks for any suggestions.  

Answer
Hi Ken,
The front axle shafts are turning all the time.
The left one is directly connected to the differential in the front axle housing, and with the cold, and possibly thick oil in there preventing the pinion and ring gear from turning, the spyder gears are probably what you hear working.
When you engage 4X4, you activate the actuator on the right axle shaft, and with it engaged, the ring gear and pinion is forced to turn, rather than just the spyder gears.

I would check the fluid level and condition in that front differential oil.

Van