Either one of these, but both would obviously be the most user friendly.

1. Add back the sound FX when the zombies start to spawn to warn players that the dead are rising.

2. Add a text broadcast option (Just like how you announce #'s and types) to warn players that the dead are rising.

That way people aren't completely caught off gaurd that the zombies are now roaming. I thought the sound FX was cool in the original version, but having a text telling people that the zombies have risen (that could potentially be customizable?) would be awesome.