Firstly the truck in question is a 1994 GMC K1500 5 speed 350TBI.
Ok so I’m not sure what is causing the noise I’m hearing. its a humming that I think is coming from the front differential but I’m not sure, maybe it is the transfer case but it certainly feels like its in the front end and my steering does seem affected while in four wheel drive. It only makes the noise while in four wheel drive. I have one off size tire on the rear end and I’m not sure if the actual tread circumference is the same between the front and rear tires or if any of this would really cause my four wheel drive to act up. Any help would be appreciated. I am planning on putting a new set of matched tires on it soon, so if they are the cause of the problem then that’s good news.