one speaker makes static noise

Hi, guys! Recently I noticed that when I play with my head unit's settings, that my rear left speaker makes a crackling/static noise when I play around with the volume/fader/balance controls. It's especially noticeable when I mute all the other speakers. If I use my imagination, I think I can here 's' sounds also sounding a bit static from this speaker, although I'm not 100% sure it it's indeed the case... Is this a sign of a bad ground, blown speaker or poor connection?F R A N S

1985 Mercedes-Benz 230E

320 000 km / 199 000 miles

Full MB Service History

Sorry, I thought my signature showed my setup. This is it: Headunit: Kenwood KDC-X889 Stereo amp: Kenwood KAC-8452 Mono amp: Kenwood KAC-8152D Front stage: Kenwood KFC-P403 Rear fill: Kenwood KFC-6909 Sub: Kenwood KFC-W3514DVC It's the left 6×9 that's giving the problem.F R A N S

1985 Mercedes-Benz 230E

320 000 km / 199 000 miles

Full MB Service History