DIAGNOSIS: That's the sound of the internal power supply or a cooling fan. Some units have a small fan that runs intermittently to cool the electronics, and a faint transformer hum from the AC/DC converter is normal.
FIX: First, verify it's coming from the base, not the lid. If it's a constant, faint 60Hz buzz, that's just the transformer and nothing can be done—it's a characteristic of the design. If it's a louder intermittent whirring, that's the fan and it's supposed to turn on and off.
IF THAT DIDN'T WORK: If the noise is loud, rattly, or sounds like electrical arcing (crackling), unplug it immediately. This could indicate a failing component or a loose wire. Don't use it. Contact support for a warranty check.
HEADS UP: A quiet hum when idle is typical for appliances with touchscreens and standby circuits. If it bothers you, just unplug it when not in use. Plugging it into a different outlet on a different circuit won't likely change it.