First, I would like to welcome myself to the forum.
Now time for business. I have a 95' GMC suburban with 110,000 on it. Auto trans, 4x4, manual transfer case, stock tires 5.7L. When I drive between 58-68 it has a whining sound that sounds like its coming from directly below me or slightly to the front of me. It drives fine, 4x4 works, it fades in starting about 58 or so, and fades out at about 58. At other speeds it is quiet. Any ideas? Things to check? Thanks for any help I get, if I find the problem I will post back with my answer.