Is the driver a K-55-M?
If so, Place your hand on the black plastic part on the back of the driver. If this stops the sound, then you may be able to fix the driver.
Look for the glue joint around the outside edge of that black piece. If you find that it has come loose, take a razor knife and cut the glue all the way around the black piece. Once free, lift it up just enough to put some epoxy back under the edge. Then put the piece back in its place and weight it down until the glue dries.
This should stop the sound.
If not, you may need to replace the diaphragm or whole driver.