Could be a behavior
It might be a behavior-infants often, for example, learn that people notice a 'fake cough
He might find the noise interesting, and how everybody turns to him when he does it. If he does it only one time, occasionally, seems fine otherwise, and looks at you and smiles, chances are it is. If it is happening in succession or he seems distressed, has a cough, or seems ill, i'd get him checked.