"Sound" is probably better, but since you want to convey an image there are other more evocative nouns you might try, for example, "the constant thunder of explosions and rattle of gunfire," among many other options. Which you choose is all a question of personal style and intended effect.
If you do go with sound it is "sound" not "sounds", "The sound of children playing was interrupted by the roar of a passing train." I don't know if there is a rule that governs this usage, though, or if it's yet another idiom you have to memorize.
Lastly, the idiom is "the norm", not "a norm". It's short perhaps for "the normal way of things", but I can't find anything on its etymology.