[Golf cart guy]

I hear this all the time and 99.9 percent of the time it is normal. The chargers get hot, that's why thny need to have lots of ventilation .

Transformer noise is an easy fix and doesn't mean the transformer is going bad. The shellac on the transformer has just heat cycled so many times its not longer is holding the transformer plates together and they vibrate.
Ive found chargers last 20 years plus as long as you don't leave them out in the rain.
The majority of charger repairs are right around a hundred bucks if you have some body fix it.