My Four Year Old Grandson Has Been Making Weird Noises

My four year old grandson has been making weird noises with his mouth for the last month or so. It's like he is spitting saliva though his teeth and lips. When I ask him about it, he says its because he has to. His parents are getting back together (has been a stormy relationship) in a few days and I'm wondering if the noises have to do with the uncertainty of the move. He will be leaving a home where he is dearly loved, with an uncle who is very important in his young life. Do we have something to worry about concerning the noises? Or, will this go away once he feels more secure with his new surroundings?