Alan (I think) mentioned that sometimes the speakers get banged around in shipping enough that an internal wire ends up touching the inside of the cabinet and buzzing at certain frequencies. IIRC the solution was to remove the driver from the front and move the wire.
I always had a problem with this when building speakers -- if you keep the wires short enought to never touch the sides then they're too darned short when you try to take them apart.
I ended up trying elastic bands as tensioners for the wires -- works OK if you solder the connections but bad news if you use push-on terminals
