Does anyone know how to make this sound? ?

I like Ladysmith Black Mambazo, a South African acapella singing group. One of the main reasons I love them is because they sound like a full band (complete with instruments) with beautiful musical arrangements. My question then is about a particular sound made when either a hard "c" or perhaps a "k" is said, a clicking noise almost. I've tried to replicate it but it doesn't sound as sharp as it does on the music. I thought it may have been the sound production error or an echo, but I've heard it when they're just talking. Does anyone know how to make the sound?