These noise packs are groups of short M4As designed to allow UAC to beep, rather than play a song. There are currently 4 packs, consisting of the following:
Generic Noise: These sounds don't sound like anything specific (or even recognizable). They are simply a group of noises that you might find a regular alarm to play.
Voiced Noise: These are computer-sounding voices that speak a statement, or other sounds that could issue from a human being's throat, while passing through vocal cords, but not quite as refined as speech.
Recognizable Noise: These sounds refer to good, old fashioned, real sounds, or at least close to it. Breaking glass, a flushing toilet, and foghorns are examples.
Particularly Loud: If volume is necessary, these are the crem de la crem. Each of these sounds can be found in other packs, and they are the loudest, most disconcerting, most attention getting sounds available.
More will be coming, depending on the response to these sounds.