Humming sound form the rear when I go over 35mph

Initially the car would start making noise between 45-55mph then it would stop and start up again around 70mph. when I shifted the wait of the car by turning left the sound would go away. I had the 2 front bearings replaced. still had the same issue. I than replaced the left rear bearing, issue resolved. less then one month later the car is making the same kind of noise only it starts at around 35mph does not go away at any other speed and does not stop with shifting the wait. any ideas?? Thanks in advance.