matt,
I see you are going with process of elimination starting with the tires. If you got a full size spare, you can try mounting it and test if humming still exists, or ask a fellow dubber with a 18" 5X100 wheel that you can test out. It would suck to splurge on new wheels and rubber only to find out the humming is still there. Also just throwing this out there, check if the inside of the wheel for any cupping or scallopping, you could have a lot of meat on the outside but if your lowered, our R's are known to chew the insides.
What tire do you have and how many miles? A lot of tires get noisy as they wear down, harder compound tires will make a louder noise than its counterparts.
Next culprit would be the wheel bearings. With that side jacked up, grab your wheel in the 12 and 6 o'clock position and see if theres any play, it should not move.
Rule out the tires before making a purchase. Just my 2 cents.
