Diagnosis
That's coil whine from the camera's internal power supply circuit. It's a physical vibration in the inductor or transformer.
How to Fix It
There is no user-serviceable fix. The component is soldered to the main board. Contact Arlo Support immediately. This is a manufacturing defect covered under warranty. Do not try to open the sealed unit.
If That Didn't Work
If support is unresponsive, you can sometimes reduce the noise by ensuring the camera is powered by its original 5V 1A adapter. Inferior third-party power supplies can exacerbate the issue.
Heads Up
Do not attempt to dampen the sound with tape or by blocking vents. This is an electrical fault, not just a noise nuisance, and can be a fire risk.