I'd say your speaker is cactus ?.
Mine had this issue from day 1. The supplier refunded me 100% of myoney and told me to just throw out the speaker, but I enjoy pulling apart everything far too much to throw it out.
After watching a tutorial on how to remove the waterproof casing (it will never be waterproof or dustproof again). I discovered the the speaker cone and front surround suspension was not fully glued (I assume this was a factory fault, and a widespread one at that).
I ran a thin bead of super glue around the rim of the speaker cone and secured the rubber suspension to it, let it dry, re construct speakers and case and viola!
Haven't had any further issues with the speaker since.
Fair bit of stuffing around involved to pull it apart but may we worth giving it a go if it's heading for the bin anyway.
Ollie