Usually they don't work at all, though sometimes the overheated voice coil will warp the voice-coil former (if the wires in the voice coil haven't shorted out) and you'll hear a scraping or buzzing sound as the former rubs against the magnet pole piece.
Likewise, sometimes speakers that are overdriven by boosted bass (assuming you aren't running a subwoofer), the woofer voice coil will hit the magnet structure with a sharp "snap" sound. Depending on the driver, this may also warp the voice coil so that it then scrapes on any heavy excursion bass note.
I recall this happening during tests of a quite interesting omnidirectional speaker from dbx, called the Soundfield, which bottomed its woofers when we played Dire Strait's Ride Across the River at higher listening levels. Several woofers had to be replaced to continue our tests for the magazine at the time.
Regards,
