The right answer is Palpating the neck or face.
The collection of air in the inner layers of the chest or under the skin of the tracheostomy can result in pneumomediastinum or subcutaneous emphysema respectively.
The subcutaneous emphysema is recognized by the characteristic sensation of cracking when palpating the skin, swelling. In this case, you need to remove some of the sutures from the wound and loosen the bandage.