Diagnosis
That's coil whine from the internal power components. It's not a defect per se, but a common physical characteristic of some electronics under load. The M2 doesn't have a fan, so it's electronic noise from the circuitry.
How to Fix It
Unfortunately, there's no software fix or setting to eliminate coil whine. It's a hardware phenomenon. You can try plugging it into a different power outlet, preferably on a different circuit, as dirty or unstable power can sometimes exacerbate it. Using a simple surge protector instead of a smart plug or crowded power strip might also reduce it slightly.
If That Didn't Work
The whine's pitch or volume might change with what the hub is doing. If it's managing a lot of devices or processing automations, it might be working harder, causing more noticeable noise. There's no way to throttle its performance, though. If the noise is truly unbearable and constant, your unit's components might be at the extreme end of normal variation, and a warranty exchange is your only option.
Heads Up
This noise is often more audible in very quiet rooms. It's not a sign of impending failure, just an annoyance. Placing the hub inside a cabinet or behind a slight barrier can dampen the sound enough to make it unnoticeable.