Lubricate the hardware on your door (e.g., hinges, rollers, bearings, torsion spring).  Avoid WD-40 as any lubricant used on garage doors should be silicone based.  Also, lubricate the track where the trolley pulls the door back and forth.  If the sound continues, the rollers likely need to be replaced, but other parts could be at fault.  Rollers will naturally wear down over time and will cause a squeaking sound every time the door is opened or closed.  Replacing old rollers is a quick and affordable repair, and the rollers we install come with a lifetime warranty.  Contact us, and we will be glad to help!