The laptop AC adapter makes a buzzing noise and gets very hot.
AC adapter is failing.
Possible troubleshooting steps and repair solution:
All laptop adapters make some buzzing noise and generate some heat.
If you can hear the buzzing noise only when you listen very closely, that’s normal. If you can keep the adapter in your hands and it’s comfortably warm, it’s normal too.
On the other hand, if you can hear the buzzing noise from a few feet away, and the adapter is so hot that you can barely keep it in your hands, most likely the adapter is failing and will have to be replaced soon.
The AC adapter is a sealed unit and cannot be repaired. When the adapter fails, you just replace it with a new one.