'98 Blazer front end noise

My daughter now drives this vehicle, but it used to be my car. My daughter has been telling me about a noise from the front end, and when she called me on her cellphone it sounded like a "whiring" noise, like low and flat tires make as you pull off the road, it changes with road speed until you stop. The shop we use has only been able to replicate the noise once on the rack, and when they shifted the car into 4 HI, the noise went away and now they can't get it to do it again. My daughter went home today, back to college, and she is using that trick to make the noise stop. After a few miles in 4WD HI, she shifts it back to 2WD and the noise is not there for 20 miles or so. This doesn't sound good. This car has 95,000 on it and is otherwise in great shape. Is this a transfer case problem that only a dealer can figure out and fix? Thanks in advance.

my blazer did the EXACT SAME THING. It ended up being when i'd put my truck into 4x4 one of the front tires wouldnt dislodge from 4x4. So once it was in 4x4 i'd be driving and about 10 mins into the ride id get this loud, jet plane engine like, whining noise.. when i slowed down it would get louder and louder until i stopped and it would CLUNK and stop. Make SURE (even though its shift on the fly) you keep the truck completely stopped and in NEUTRAL when changing between 4x2 and 4x4 and visa versa. good luck.

check for a front axle engagement switch on the transfer case up top with 3 vacuum lines coming out. those will stick and allow the front diff to stay engage all the time. with out the front drive shaft spinning the front axles just free wheel and grind up the engaging sleeve in the front diff