Sounds like you either have a jack that has broken the solder connections to the circuit board or a piece of a plug came off and is stuck inside the jack or else you have a jack that the plug is just too loose due to age and slight bending of the parts that make contact inside the jack. Of course it might just be a bit of corrosion in the jack. I am assuming of course that the “popcorn” sound goes away when there is nothing plugged into that jack.