I have a 240 and I began noticing a humming/buzzing sound from the front driver side starting at about 70 km/h. As I increase the speed to 90 km/h the sound decreases, but then intensifies at greater than 90 km/h. Had the wheels rotated and the sound now comes from the right back side (presumably the same tire). The mechanic said the tires looked fine and all wheel components were tight. Any ideas what this could be? Rim? Tire itself (Make: General Tire - 3 yrs old; approx 30 000 km)?

You have run over one of the harmonizing members of an acappella group. Seriously, there is something wrong with the tire. If it thumps at all that is a dead giveaway, but odd noises are indicitive of a problem. You can do two things. One is to replace the tire. The other is to wait until it is bad enough to tell what is wrong with it, then replace the tire. Experiment with different wheels and rebalancing if you want, just to convince yourself, but if the tire is bad and you wait too long, you will lose the wheel bearing. DAMHIK.