I’m not sure what you mean by a “buzzing” noise, but noises can be generated from many drive train components. I’d start by inspecting the bottom bracket/cranks, the pedals, and the rear derailleur pulleys, then check the tightness of the chainring bolts and the rear cogs.
If you don’t hear it when coasting, it could be that one or both of your derailers are out of adjustment and there’s some friction from either the cage in front or somewhere in the system in back. I’d start by making sure all your shifters and derailers are adjusted correctly.
Among other things, check the B-limit screw setting on the back of the rear derailleur. The buzzing might be due to grinding of the jockey pulley on the rear derailleur.
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