Sound like it could be air under the skin, called surgical emphysema.or crepitus. Usually happens when there is a cut near a joint and when the joint articulates it sucks the air in under the skin but can be second to infection. You need to sort the underlying cause and decide if it needs intervention.   edit to addd link although this is a bad case http://dogscatskidslife.blogspot.co.uk/2005/11/subcutaneous-emphysema-in-canine.html