Sheep baa, cows moo and alpacas hum. Different animals have different voices, but basically it is a "mmm" sound. Hums are often comfort noises, letting the other alpacas know they are present and content. However, humming can take on many inflections and meanings, from a high-pitched, almost desperate, squealing, "MMMM!" or frantic question, "mmMMM!" when a mother is separated from her offspring (called a "cria,") to a questioning "Mmm?" when they are curious. Alpacas make other sounds as well as humming. When danger is present they sound an alarm call, a high-pitched, shrieking whinny of sorts. Some breeds are known to make a sound similar to a "Wark" noise when excited, and they stand proud with their tails sticking out and their ears in a very alert position. Strange dogs – and even cats – can trigger this reaction. To signal friendly and/or submissive behavior, alpacas "cluck," a sound possibly generated by suction on the soft palate, or possibly somehow in the nasal cavity. This is often accompanied by a flipping up of the tail over the back.

When males fight they also scream, a warbling bird-like cry, presumably intended to terrify the other combatant. Fighting is to determine dominance, and therefore the right to mate the females in the herd, and it is triggered by testosterone. This is why males are often kept in separate paddocks – when two dominant males get together violent fights frequently occur. When males must be pastured together, it is wise to trim down their "fighting teeth," large fang-like teeth whose name explains their function.

A male in the act of mating, or hoping for a chance to mate, will “orgle.” This orgling will help to put the female in the mood, and it is believed that it also helps her to ovulate after the act of mating. Orgling is good for all parties concerned.