Originally Posted by Yoytoda
Its prolly the tcase. mine whines. its the gears. in 4lo the gears spin as if you are in 4hi at high speeds. there isa gear reduction in 4lo but the input shaft is spinning the same speed as in 4hi.
Ex. if it whines at 15mph in 4lo then it will whine in 4hi at 45mph
Like in 4th gear the ratio is 1:1 through the tranny so 2000rpms on the engine the tranny turns 2000rpms. When in 4x the tcase will run other gears to turn the front drive shaft. so 2000rpms in 4hi and 2000 in 4lo will both whine but in 4lo the gear reduction adds noise and the wheels turn much slower. with 4hi your going much faster so you dont notice the noise much.
Perfect explanation, I was going to allude to the same thing, just explained differently. It's normal, dont worry about it... gears moving.