Front Differential Noise

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.

Are you driving on dry paved roads with the front axle engaged? You’ll hear noises right up till something breaks doing that.

You need to hurry to get the matched set of tires. The noise is probably the differential complaining about the difference.

It the differential stared to “complain” a while after you put the unequal tires on, it may now be permanent. Be prepared for that. If it did immediately and it hasn’t been too long…the gods may be with you. Regardless, I would service the front, rear differntials and transfer case when I put new tires on. The noise you hear could be wear and more metal is being " relieved". Check the fluid levels NOW.

Having just been through a rear differential failure and rebuild that took 3 tries to get it right, I fully agree with the posters here. Verify oil level and don’t use 4wd until you change tires. May the force be with you…

Also check the front constant velocity joints.