I have a pretty loud humming noise that sounds like it may be coming from the rear. It seems to be speed-dependent and not RPM-dependent. The noise changes with speed and it can be heard as low as probably about 20 MPH. My tires (particularly the rear ones) are near the end of their life spans so I thought perhaps could be them. I just wanted to get some feedback on here to make sure I don't have a larger problem.

 

I did find a couple of posts on here regarding bearings, which is really what I figure the other option is. I'm not getting any other sounds though, so is that a possibility? Also, if it is bearings, is that an urgent issue on these cars?