Just recently out '05 Tucson has developed a low pitch sort of hum when going between 40-50mph. The best way I can describe the sound is like the tires have been swapped for some aggressive snow or mud tires. I rotated the tires and even used the spare and the sound is still there. Nothing "appears" loose, broken, etc.. The alignment feels good and the tires are new-ish with only 2k on them.

Any ideas?

Steve