Like MichaelDay said, one or more of the wheel spokes may be contacting the brake caliper. If you can tell what wheel is making the noise you could take it off to visually inspect the back of the wheel and the caliper for signs of rubbing. If you're lucky, you may even be able to inspect the caliper with the wheel still mounted and find a place where bright metal showes up from the rubbing.
A bit of grinding or filing may be all you need or perhaps a spacer on the hub.
In any case, get a little dirty and give yourself the pleasure of solving this issue.
I just re-read your original post. Rotors, spindles, wheels and such can be bent by impacts such as potholes. This can cause a pulsing noise when braking. If you have your wheel off, spin the rotor and look for runout of the rotor. If you can detect the caliper moving slightly in and out then you have a bent rotor.