Capt. Rich Tippelt of the Town of Beloit Fire Department says investigators don't suspect arson and don't suspect any foul play.
Firefighters found two garbage trucks engulfed in flames and two partially on fire when they arrived late Tuesday at Rock Disposal.
Tippelt tells The Janesville Gazette the fire apparently started in the cab of one of the trucks.
Rock Disposal owner Robert Klimoski says a fifth garbage truck was damaged and will need minor repairs.
The company has a fleet of about 25 trucks.