After a quick search, I see @beep was implemented for the specific purpose of notifying a user when a long-running query had ended. However, since it's tied to the default system "critical stop" sound, this doesn't really accomplish the task. Call it "alert fatigue" if you want, but I hear this sound all the time. It could mean anything.
Please implement a setting to allow users to change it.
I will open a ticket. However, consider it low prio since this is the first time it is requested.