Popping Sound From Opriginal Sub

[Dupont24]

recently i started getting a popping sound from my original sub and from my rear left spreaker when i powered on the stereo. the sub is original and the back decf speakers aren't. i originally thought that there might be a ground leak or some thing...i have no idea...i am driving a 94 sc300 with premium 12 disk system.... i9f anyone has any ideas that wiuld be great