Buzzing sounds can come from loose wiring, a failing contactor, or an electrical component issue

https://trustedsamedayac465.rivetgarden.com/posts/affordable-ac-repair-in-winter-haven-how-to-find-the-best-value

Buzzing sounds can come from loose wiring, a failing contactor, or an electrical component issue. For safety, turn the unit off and have it inspected promptly.