It's very likely that the speaker has been damaged. Such as a physical crack on the membrane. As it vibrates when it plays, the pieces crash against each other and that's the cracking sound you hear. You most likely need to replace it. It shouldn't be too expensive.
2 
It's very likely that the speaker has been damaged. Such as a physical crack on the membrane. As it vibrates when it plays, the pieces crash against each other and that's the cracking sound you hear. You most likely need to replace it. It shouldn't be too expensive.
Funk Addict さんによる