I recently built up an '02 NRS frame, getting most of the components (xt cassette; sram chain, rear derailleur & chain) from my hardtail. I bought a used set of Mavic Crossmax XL's (disc) wheels and Avid mechanic disc brakes. I have taken it out for 6-7 rides (between 55-70 miles total).

I recently replaced the tires with a set of Nokian Boazobeana tires and during the last two rides, I have noticed a buzzing noise coming from the rear end when I stop peddling (not always, but a good bit). The noise stops when I start peddling--given that the noise stops when I start peddling, I figure that its freehub but am not sure. Any suggestions on what I should look for? Thx.