Well its a known issue. My galaxy tab plus also had the same thing and my notes charger as well. But it will self resolve once u put it in another plug. Its transient for me, sometimes
It comes and at other times its gone.
Sent from my GT-N7000 using xda app-developers app
These chargers use a switched-mode power supply that usually runs well above the audible frequency range typically several 100KHz. Some designs cope with a light load such as close to end of charge by cycle skipping and this can bring the frequency down into the audible range. This is not a problem per se but may be audible if the transformer is not totally encapsulated. It's like the hum you may have heard on a 50/60Hz transformer but at much higher frequency.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?