Why is the left side have no sound?

When I turn my headphones on, there is no sound coming out the left side of the headphones. And if there is sound, it is very shaky and ins't even from the sound source, when I used the wire on the headphones, there was sound coming out the left side but it was very shaky. do I need to open it and replace something in the headphones? I think it is soundthing with the speaker and the bluetooth.