What's wrong with my subwoofer?

In my car I have a self-contained subwoofer (amp and speaker in a box with a tube). The speaker had been working fine for a while, and just recently it stopped producing b. It will instead crackle/hiss. I noticed that it is recieving the audio signal, because the beat of the song is coming through the speaker, there is just no sound; only crackle. Also, the cone of the speaker is in tact and nothing looks broken/disconnected.