My 2000 has rubber flap-like things inside the front wheel wells covering some holes leading to the engine compartment. They're held in by those infamous plastic expansion clips. Well, a couple of the clips came out, and the rubber starting flapping with the breeze. It was noticeable as a noise at a certain speed.
So, check out all of the rubber and plastic trim inside the wheel well to rule that out as a possible source of the noise.