Guinea pigs "chattering" type noise?

  I have 2 male guinea pigs, aged 1 year, they sometimes make a chattering type noise ie they move their mouth/teeth very quickly, producing a kind of chatter. I just wondered what this means/signifies?
Guinea pigs can be vocal when they see their owners or something they like. It's completely normal.
Well i dont speak Guiena Pig but if they chatter that means they want play time or they are hungry !!!!!