My 5 month old heeps making a gasping for air noise sometimes when he takes a deep breath in I don't know if he just found a noise or something wrong?

Try This. If you turn the baby onto his tummy and the noise disappears, coming back when he is on his back...You have tracheomalacia which is an immaturity of the trachea or windpipe. This is noisy, but generally benign. Babies usually grow out of this immaturity. If so ask your doctor.
Problem Breathing. Baby should normally breath not gasping or noisy breathing.He could be sick.Pls. Have him examined.If he is ok and the noisy breathing persist at age 1 to 2 years you call it bronchomalacia which will eventually disappear af age 2 years.
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.