Muffled speakers, whats wrong with them?

Okay so I have 'Altec Lansing AVS300' speakers . So theres one large speaker then two smaller ones. For a little while now the speakers sound really muffled, but some beats and some parts of songs sound normal and clear. We are hopefully getting new speakers soon anyway; they look ancient in our house. But for the time being, I'd like to know if theres any way of fixing them? The main speaker and the right speaker whcih controls the volume dont make any noise, but the left speaker works and the volume controller works for that speaker. I know how to take other speakers apart but these dont have screws and wedges dont open the back. Please help? Also, I can provide with more information if you ask!