GMC jimmy buzzing noise/vibrations at 30mph+?

Ok so recently I've been having a wierd problem with my 99 4x4 GMC Jimmy. The car itself runs fine. However when I hit roughly 30mph, a wierd buzzing/humming noise starts to come from what sounds like the left side of the car. At higher speeds the buzzing is a bit louder. It also vibrates the floor a bit. However when I am turning to the left, it almost completely stops, but as soon as i straighten out again, it's right back to the buzzing. Turning to the right does not stop the buzzing. Any ideas on what it might be???