2004 Avalanche, 5.3L, two wheel drive, 143,00 miles. Has a humming sound when going about 15 mph or over and slightly turning to the left or right but the sound is not present when the truck is driving straight. The sound can be described as a low humming, whirring or very light grinding and it actually crept up on me, getting progressively worse, now it's noticeable to anyone sitting in the front seats and it seems like it's coming from the front end someplace. It's not super loud but noticeable. It's not a clunk, it's constant when present and does not change with varying speed but it goes completely away when the truck is going straight and no pressure is on the steering. The steering is pretty tight, and when the truck is parked you can turn the wheel all the way to the left or right without any squealing and the wheel movement is smooth. Replaced the left wheel hub and it made no difference. Any suggestions? Thanks for your time.