2003 Explorer with a Humming Noise

[dtroche72]

So Iv'e looked through the different posts and see that it could be either a bearing or differential issue. Anyway to tell which one? I hear it when I accelerate. Get louder around 40-60 mph then quieter after 60. Hard to tell where its coming from but if I had to guess I would say passenger rear.

 

[Number4]

Most likely a bearing. You could jack it up and check for obvious play. If you detect play you'd best not drive it. Most bearings fail with no noticable play, this is due to the allowable tolerance being very small.