Very distorted sound (even system sounds)

My speaker started sounding awful all of a sudden. It has not been dropped, submerged, hit or whatever. All sound from the speaker are affected, even system sounds like power on/off, battery status and so on. I tried updating to the latest firmware, factory reset, even hitting and shaking the speaker, but with no success. It doesn't sound like some debree is touching the speaker, but rather software/hardware fault. I have still not disassembled, so I cannot be sure.