A faint hum from lighting is common and usually harmless, but a louder buzz, or one that's new or getting worse, is worth paying attention to.
The most common cause is an LED globe that isn't compatible with an older dimmer switch. The dimmer's electrical waveform can cause an audible buzz in some LED drivers.
Buzzing can also come from a loose wire or fitting vibrating slightly with current flow, which is more of a concern and worth having checked.
Downlights with a separate transformer (common with some older halogen-to-LED conversions) can hum as the transformer ages.
If it's one light and the buzz is faint, try a different, dimmer-compatible LED globe first. If the noise is loud, coming from multiple fittings, or paired with flickering or warmth, get a licensed electrician to check the wiring.