When pressing a note on a keyboard, it may make improper sounds either pitch or sound like it is playing multiple times

Using the improper keyboard, or a power strip that has too many items plugged in can cause the improper current to be drawn by the keyboard. This can cause problems with the sound output. Double check that the correct adaptor is being used, and also try a different outlet (on a different wall or room if possible to make sure that it is not the outlet or circuit that is causing the problem.