The mbira, an African musical instrument, is also known as the 'thumb piano'.
Notice that some of the players have placed their instruments inside some hollowed-out gourd that looks like a giant bowl placed vertically upright. This gourd serves as an amplifier to the mbira, helping it project.
Hear the buzzing sound? That's made by bottlecaps attached to the amplifier. This is not a sign to say that an instrument is 'malfunctioning'. African players like this kind of sound on their instruments, in their music.
Joker who spends his free time milling around NUS pretending to be a student...