knocking sound on one side of the woofer domes

[ragwo]

The voice coil is actually separated from the membrane? That's a new one. Are you able to glue it from the outside where the short red line is drawn? I wouldn't use a glue with much elasticity, the membrane and voice coil should be firmly connected to each other. Some good quality two component glue or super glue should do the trick. Please keep us updated on the progress! Good luck!