I have a 2005 5.3 Chevy Tahoe. It has about 119,000 miles. About a month ago I noticed a humming sound coming from under the hood. So low that I must turn my radio off and let my windows up to hear. I hear the noise as I accelerate and the noise speeds up as the truck speeds up and slows down as the truck slows down. My power brake booster or hydro booster had a bad seal and I thought that was where the sound was coming from but after changing it out, the noise was still there. I was also told that it was coming from my brake pads because they were too dry on the back side and needed greasing with the grease you put on the back side of the pads during installation. I went ahead and installed new brake pads while I had them off and the sound was still there. I've inspected my tires to make sure the there was nothing rubbing and the tires look great... I'm really at a loss. What makes it so bad is that I only hear the sound when driving and can't duplicate the noise... The only thing I can add is that I just noticed is that my cruise control is not working. Not sure how that unit works but just throwing it in for whomever may be able to assist. Thanks in advance for any assistance.