dum dum also called thumb gum - go to the electrical isle at lowes/home depot. it is a gray soft clay-like brick. Brake a piece off, roll it into a snake, put it around the stud, tighten, it smashes and seals. Similar in concept to plumbers putty. Thumb gum is used in houses to seal penetrations thru siding (hvac line sets, hose bibs, cables, etc.)