I'd start with checking the plastics for loose fasteners or very near contact with metal
parts.
That shouldn't take more than applying pressure in areas to see if the noise stops.
I've certainly heard plastic vibrate like that, making a buzzing sound.
From there I'd inspect any lightweight metal
parts. The heavier the part, the more likely it'll make a lower frequency sound, more of a rattle than a buzz.
Anything that's safe to put a hand on while running is what I'd do before getting any tools out. With the design of the forks, maybe put an ear near those. It could be spring making that noise.