4 cylinder engine inherently have a high-speed vibration - that's why most modern engines (B234F, Volvo white engine, most of the competition) have balance shafts. If you are talking about a noise that the engine did not have in the past, you should look for things that would cause a minor imbalance like cooling fan, missing torque converter bolt, failing crank damper (wobbling).

Can you duplicate the noise in neutral? Cranks bearings could be worn and causing a faint knock that sounds instead like harshness.