A warped rotor will produce a similar sound. You can confirm that it is a rotor by lightly pressing the brake pedal while moving fast or slow. At a fast speed, there will be a loud noise. At a slow speed, you will probalbly feel the brake through the pedal.

sounds like its time for rear shock
my wagon would cup the heck out of the tire making
for a loud ride,

if your car has 70k+ on it replace the rear shock
should solve the problem

Here are some things that I have run into similar to your description: Your description of a "humming" sound does not seem to indicate a problem with a bent rim or misalignment. If it were a bent rim, you should experience a vibration and not just a noise. If this humming started after you had 7,000 miles on the tires, then the only possible tire related thing to check is for some type of visible irregular wear on the tires that might cause a noise, like a cupping or feathering of the tread elements. If you do have some unusual kind of wear, then you will also need to troubleshoot the suspension to find out why you have this irregular wear. Are you rinding on a newly re-paved roads? in some cases, driving on newly paved roads can result in some pretty loud noises from some tires. Good Luck.

Sounds are fairly hard to describe in words, but "humming" at a low tone is usually related to a bad wheel bearing... typically if the humming is louder when turning in one direction (coming from the inner wheel of the turn) then likely the bearing needs to be replaced, or you can often 'temporarily' get away by repacking it (regreasing it).