It is actually possible to set up the brake pads so that they're not in contact with the rotor (even with single sided piston calipers). Avids are of course the easiest to adjust, either mechanical cable or hydraulics.

Find the right angle to "peek" at the rotor & pads from the front view or rear view - with the rotor in between you and a bright background, you should be able to see some light come through in between the pads and both sides of the rotor. In a single piston actuated caliper, the "light gap" between the rotor and the fixed pad should be minimal (paper thin)... to prevent too much rotor warp during braking. On twin piston actuated calipers, the "light gap" should be evenly spaced with the rotor bang on the middle.

If the rubbing noise is intermittent, your rotor is off-true. "Peeking the light gap" should show you where the wobble is (place a chalk mark on the tire). If the wobble is small (1mm or less) place that location opposite and 180 degrees away from the caliper, and then give that rotor section a controlled firm push. Try not to touch the rotors with oily fingers, use a clean rag. Recheck with the light peek test, easy does it, little by little. Don't over do it or you could create another opposite wobble and compound your problem.

If you have a major rotor wobble (from something hitting the rotor during in a crash, while riding or while parked) take it to your LBS for assessment. It may need to be replaced.

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