Try a visual cue. If your son makes these noises at the supper table, for example, print up a laminated card with either a picture of a finger help up to the lips in a "shhhh" sign, or the words "table conversation in words only, please. no chants or noises". Just hold up the sign (make it really bright and clear).
Make a hand signal that you and he recognize, like hold your hand open and gradually bring your hand to a closed fist position (not in a violent way, but much in the same way a choir conductor might close his hand to signal a choir to stop). Role play with him to practice silence when he sees that sign.
See if your son can respond to that kind of cue. Try teaching him there is a place for fun noises and chanting phrases, and a place for quieter conversation. That might help you determine if he's just snakes and snails and puppy dogs' tails, or if he needs some professional intervention.
Also, make sure that you are asking him to stop for the right reasons. Not just when you're doing laundry and could just use a break, but when people are talking, or watching tv, or eating, or when it's time for him to be reading or calming down for sleep. Make sure his active behavior is allowed, just at the right times, and in the right circumstances.