I have a 2000 4x4 ext cab GMC sierra and it has some kind of high pitched chirp/squeeking sound coming from what i believe is the drive train somewhere. I have sprayed all the u-joints with WD40 and still chirps. The sound seems to coincide with the rotation and speed. At first it was hit and miss and now it is a constant thing. The drive shaft that goes from the transfer case to the differential can be turned by hand about 1/4 to 1/2 and inch, is this normal? I have not yet checked the differential fluid either. Any ideas of what it may be?