What Causes Constant Clearing Of Throat In A Child?

My five year old grandson is constantly clearing his throat. My daughter-in-law is so upset. She thinks it is a tic. They found mold in the bedroom and they have 3 cats. She had him tested for allergies but nothing came up, only that he may have a ashma problem when they heard him breathe. Next week, she is taking him to an ENT and she is thinking of having him scoped. I told her to try zyrtec and see if that would work. Please help.e