Alot of people complain about nighttime servers, but since Zombies can see much better than they hear, at daytime you are much more likely to be attacked by any zombie within a 100m range. Unless you are sprinting, you usually only agitate zombies if you are moving crouched or crawling in a 3-5m range. And if you need to, BE STILL. At night I have had numerous Zeds crawl right up to me, bumping me, and going around me as long as I didn't make a noise by moving. (there are always exceptions but that is life in Zombieland)

Also,

Noise agro from firing a weapon are cumilitive.. So you can safly snipe one at a time from a distance away. But the more shots you take in less time will widen the noise agro more and more. So one shot at 100m will not agro anything, six shots fired reapeatly will attract all zombies within that 100m + ....