When I'm rolling under 30, I can feel a bump, bump, bump, from the front wheel with every rotation. The bump goes away immediately when I apply any pressure to the front brake lever.
Could be a bad tire, bad wheel, bad wheel bearing, bad rotor, bad caliper, bad pads, bad fork internals, stuck pad, sticky puck, neck bearings.....hope this helps.
It is a very warped right front rotor. The rotor hits the caliper, making the bang. When the brakes are engaged, the rotor is centered, pulling it away from the caliper.