Yep, try batteries and if it does go away then it is your power adaptor . Roland equipment is very particular about power supplies , look at the power supply input or on the bottom of the machine and it should say EXACTLY what power adaptor model is required . If you are using a different type it will hum or not even work . It could also damage it becuase the hum is probably meaning it is getting too much power or the polarity is switched to the wrong setting . In America the SH-101 uses the AC-120 adaptor , anything else and it will hum and do other weird things .