I had that issue last week. Took the drums off, inspected them and noticed the cable that is for the adjuster retainer was broken. Replaced the adjuster, retainer and the associated clips for it, adjusted them up and mines been good to go since.
Drum brakes are a pain in the way that they need regular maintenance and adjustment. I pull mine off once every couple months to inspect and service.
Also have a look at your front knuckles where the pads sit. Mine actually have spots where the knuckle has worn away leaving grooves that could cause the pop sensation