You have not indicated whether the noise is in time with crank rotation, but I assume it is. If you think about it that already eliminates brakes/wheels, rear cog/hub and chain, because the wheels only rotate in time with cranks on a 1:1 gear, and the chain never does. Check out of the saddle to eliminate seat/post, but a more sustained sound rub/grind is far more likely to be between two moving parts, such as within the BB or pedal bearings, than between parts that are not meant to move.