Fan buzzing

My fan has started buzzing at medium to high speed (recording: https://cdn.discordapp.com/attachments/201803114049699849/886987319637336084/Monday_at_09-49.m4a)

I took it out and made sure it was clean and nothing was caught in it, so I am concerned that it may be off-balance. I can tolerate some air whooshing sounds but the buzzing is quite annoying. Anyone know if this is a known issue or there’s a way to fix it?

Hi, could you fill out a support request around this?