Is it a noticeable pop that runs with the beat? If so, blown speaker. Turning the volume up and clipping your signal = easily blown speaker.
A "blown" speaker doesn't mean it was too loud and blew up. It means the coil inside was receiving a dirty signal. In between notes the coil is "resting" and releases it's heat from the electrical input. If it's receiving a dirty signal or static then it never gets that rest period. The end result is an over-heating coil that loses it's proper shape. If it loses shape then the acoustic properties change....you might end up with "popping" instead of bass.
HowStuffWorks "How Speakers Work"
