It could be one tyre that is at fault. When I first got my Volvo S40 it was very noisy. I discovered that one of the tyres had a twist to it. Must have been in the steel belts. Tyre fitter spotted it right away, I replaced it and had no further noise problems.
I run my Jazz with elevated tyre pressures, front and back, and it is no noisier than at recommended pressures, just a little firmer ride.