Dryer exhaust vent ducts (the big silver metal duct in back of dryer that leads to wall) should be checked at least once per year. Even if you regularly clean out the lint trap in the dryer, lint and debris build-up can still occur through the dryer exhaust and will build up in the exhaust vent duct. This duct should be cleaned out when inspected to avoid any potential fire hazards. And don't forget to inspect both ends of the duct! Check to make sure the exhaust vent has a flap or grid over it to block unwanted intrusion from birds or other critters!