With 0 master volume, still get sound
(On a somewhat similar note, someone said that the siren noise was almost constantly reproducible by having three people spam the unbreakable bell inside of a time warp.)
That IS an helpful information! Because it means, that the siren noise is actually an buffer overflow (coders forgot to check the boundary of a buffer so new data is written to a location which is already reserved for something different) when too many sounds are played at the same time.
You can get it to stop by either restarting the client, or go into your sound mixer panel in windows (click the speaker icon in the task bar, click mixer at the bottom) and turn down or mute the individual volume only for GW2. That way all other sounds such as PC system sounds, music, ect still work.
~Surrender fiend and you will get an easy death
~I could promise you the same…but it would be a lie…