I have a 02 with 190xxx on it and I started to notice when im in 4x4 and cruising in 4th at around 1600 rpms theres this weird whinnying noise but when I disengage 4x4 the noise goes aways. Any help with this would greatly be appreciated. Few more details the noise as best I can tell is coming from the driver side and it is very faint and is just at around that rpm any more or less and it goes way.

 

That sounds like it'd be a bit fast for cruising in 4wd. That is, for it to be quiet. Chain driven transfer cases aren't known for quiet smooth operation above 35 mph, after a few hundred thousand miles from my experience. Always a good idea to check front drivshaft, make sure all the bolts that connect it to the t-case are good and tight, give the yolks a wiggle to make sure no bearings are about to totally fail. Also check front differential fluid and level, along with t-case.

 

Make sure the transfercase is full of clean lube and check all the front u-joints and the double cardan joint for any movement or possibly needing replacement. Can you tell with the window down if its coming from the axle or the transfercase?

 

Really check out the front driveshaft. Its right underneath you and could be the cause of the sound you are hearing, especially if its faint.

 

Do you cruise a lot in 4th gear and 4WD? Perhaps it is just normal sounds from a chain drive, planetary transfercase at high rpms, and you have just noticed it. Anytime I have driven over 35 or 40, in many different makes of trucks, the transfercase made some noises.

 

I mainly just use it in the winter and I will try checking all of that this weekend thaxs for the help, and telling me where to look