It sounds very muted and has a bit of crackling noise on pretty much all tones. Could it be a connection issue, or broken speaker, or amplifier issue?

 

I would say it could be all three so inspect the speaker? Door panel is easy to take off.

I suspect though the amp. Lots of people have had issues with their amps. A loose conmection could be it too but why would that be?

 

sounds like a speaker issue