Charger Buzzes when plugged into the Adapter Converter

Im in England currently (From the USA) and am using a "DYNEX" converter adapter to switch the electric current down so I can plug in/charge my Macbook Pro and iPad.
It works, however the charger buzzes pretty loudly and gets hot.
Thankfully I brought two, one started smelling like melted plastic and stopped charging altogether. That particular charger has faulted at home before (back in the USA), so I'm not sure if it died because of the converter or because it's just faulty.
I have plugged in the newer charger and it also buzzes, but I'm really worried to keep it plugged in because I don't want it to fault out too.
Is it normal for it to buzz like that when plugged into a converter adapter?

The question again, why are you using a voltage converter?  The Apple charegers are all rated for 100-240 volts at 0-60 only need a plug adapter to convert the US HEMA plug to the UK two round pin plug.
Adding a voltage converter is adding one more failure point into the system.
I have used mine all over Europe with no issues.