I have a hum in my 97 blazer 4x4. The hum happens when i let my foot off of the pedal at any speed from 15 to 50 mph. As soon as i put the slightest amount of pressure on the pedal, it goes away completely. I have looked and searched but I havent found anyone with these symptoms. Any help would be appreciated. Im thinking its the Ujoint but it doesnt seem to have any play, im wondering if its seized up maybe?

 

I just wanted to add that cornering doesnt matter. I dont believe its a hub.

 

Any vibration with it? I would suspect u-joints also. When you hear the hum put the car in neutral and see if it goes away

 

I forgot to mention that it doesnt go away in nuetral, and yes i do feel a slight vibration with the hum.

 

Classic description of ring & pinion gear noise. If that's what it is, the damage is done and requires a new ring & pinion set. This video explains how to set up a differential so it will not howl: