That command that I gave you would disable all installed scripts. Since it's still happening even with the scripts disabled, then it's not a script, but rather a setting in mIRC.
At this point, I would suggest uninstalling mIRC, then downloading a fresh version from
the download page , then install the fresh version, but do NOT have mIRC maintain your current settings. This means that any settings that have been changed will be lost, but you'll be starting with a fresh installation of mIRC.
While I can think of an option for the beep sound when you voice someone, I'm unable to think of where the Commands menu could've been hidden.