run your hand over the tires, are they cupped? tires tend to get cupped if they're not rotated frequently (~5000 miles), or if your shocks are worn.

tire noise is also caused by the design of the tread - if there are large grooves and blocks in the tread, the tire will emit more noise. look at a touring tire and you'll see thinner cuts and grooves, compared to a "summer" tire.