2000 Chrysler Cirrus Humming noise

My cirrus has a humming noise coming from under the car somewhere. I notice it when I go 35 miles an hour or faster. When going 50 miles an hour I tug it to the left and the noise gets louder. If I tug it to the right it gets more quite. I brought it to a repair shop and they replaced the right wheel bearing but this did not help. They checked the tires and the whole front end twice and could find nothing wrong and gave up. I thought maybe it could be the left wheel bearing, or one of the rear wheel bearings, or maybe even the transaxle carrier bearings. Could you help me weed out this problem? I know my car has high miles but it has been well upkept. Dennis.