What was found
AFTER TAKEOFF THE CREW REPORTED THAT THERE WAS THREE LOUD POPS DURING THE LANDING GEAR RETRACTION FOLLOWED BY A NORMAL GEAR UP INDICATIONS. THE CREW ELECTED TO REPEAT A LANDING CYCLE WITH SAME RESULTS. THE CREW RETURNED BACK TO THE AIRPORT FOR INVESTIGATE. THE MAINTENANCE CREW TROUBLESHOT AND DETERMINED THAT THE LEFT MAIN LANDING GEAR UPLOCK SWITCH WAS DEFECTIVE. A NEW SWITCH WAS INSTALLED. OPS CHECKED SATISFACTORY. THE AIRCRAFT WAS RETURNED TO SERVICE.