I have heard this question a few years ago... the answer i think it was somsing like chenking the weapon via the "fire" eventhandler... and if it is not an Suppressed gun... you are making noise!!
=P im not good for this.. but maybe this will help
add the exection of this script on every eventahndelr units you want to chek...
and in the script must be like these
? ! _unit hasweapon "hk" : [] exec "your script here.sqs"
exit
or try whit some other guns
? ! _unit hasweapon "hk" or ! _unit hasweapon "ak74su" ETC : [] exec "your script here.sqs"
im not the wizard
you are