You're probably feeling the effects of
chordal action.
We like to think of chain drive like a pulley system, but in reality sprockets aren't round pulleys. Instead, they act like polygons with the number of sides equal to the number of teeth. That means the driving radius keeps changing, and therefore so does the relative speed of the chain and wheel, producing tension changes felt as vibration.
This is 100% normal, and one of the reasons that chain drives in machinery has a characteristic chain whine. Your system moves slower and so the whine is more of a buzz.
Better chain lube muffles this to an extent, by dampening the small shocks of changes in chain tension, but isn't magic.