One at the stations (our radio complex) does something similar, but they are too cheap to replace it.
As above, MOM is correct, loose wires, if the speaker moves. Same for the blown speakers.
However, there is one other possibility.... that could be that the stereo's audio portion may be bad. If you have no heard this on another stereo or radio, this is possible.
Sometimes, if you are near a RADIO or TV tower site, that can happen as well. You can mistake an interfering station with static. AM/FM/VHF Radio/TV - all levels of frequency they make for interferences. Yes, CB's can also do this.
My main thought, Did you have the problem before? or did you put another radio/stereo in the same place as the current one? If you did not hear any problems, it is the stereo.
I hope you didn't buy a used one, that was bad. If it's new, take it back, if it is not a station interfering.
