Faulty Rollers

• Dryer's drums are equipped with rollers, which are small wheels that enable the drum to rotate in a circle as the drum spins. Over time, rollers can wear due to excess use. When this happens, the drum can drop down from its position in the cabinet and create a gap between the drum and cabinet that's often wide enough for clothes to become trapped. As the drum spins, it can leave black marks on clothes that are caught in the void. Clothing that gets stuck in the gap and dangles over the blower can receive burn holes from hot air that's being pumped in.
  
  

Worn Gliders

• Covering the outer edges of a drum is a set of gliders. Gliders are shields that protect the drum from rubber against the cabinet during rotation. They're made of either nylon or plastic, depending on your dryer model. Just like rollers, when gliders begin to wear, they can also cause a space to open at the rear of the dryer that contacts the drum. If a piece of clothing enters the space while the dryer is spinning, it can produce black marks and burn holes on clothes.
  
  

Stationary Drum

• A dryer drum must turn constantly to evenly dry clothes. If a defective part prevents the drum from spinning, such as a worn belt or burned out motor, clothes remain on the drum's bottom even as the hot air is pumped into the drum. Without the ability to tumble, clothes in direct access to the blower's hot air can scorch and burn. As you remove clothes, you will discover black lines and burn holes on items that had hot air constantly blowing on them in one spot.
  
  

Damaged Baffles

• A drum typically has at least two plastic or metal baffles that protrude from its surface. Their purpose is to help clothes dry more consistently and to discourage them from bunching as the drum turns. A baffle can crack and split if it comes in contact with a belt or sharp object, such as a key, accidentally placed in the dryer. When this occurs, clothes can become damaged as they get hung up on a baffle's jagged edge, with black marks and burn holes both likely.