*I lost the warranty when I moved into a new apartment.
there may be some other reasons.
please check the shape of membrane. if it is concave,that might be the cause.
i was confronted with the same rattle problem with my DT931, and later i found the problem resulted in the membrane. the shape of membrane shall be a heave sphere. and my DT931 had a concave membrane. obviously the membrane will be in contact with the bottom and that is the reason.
i had my friend Tear off the membrane and restick to the unit. and in China, some friends even retried recovering the shape of membrane through huffing breath.
Thank you so much everyone. Found the last hair. It was white, probably from a cat or something. This has been annoying me for months.
Guys i need your help. I have the exact same problem, i opened the driver and i saw white "hairs" but i think it was part of the driver because they were stuck. I removed 2 of these, but i left one because it was stuck and i didn't want to damage the driver. I still have the problem though...