This is for the people like myself, who usually play PSO or other games in general with 0 sound. But with this game there is one exception, the extremely great add-on that Soly has granted us, the rare drop sound. The rare drop sound is a little ping to let you know if a rare drops, and it is extremely helpful for the AFK farmers like myself that could accidently or possibly miss a red box.
Now for the super easy short part, go to your main PSO folder and navigate to the OGG folder which can "usually" be found at c:/ultimaPSOBB/data/ogg (C drive > ultima folder > data folder > ogg folder).
It should look like this once you navigate there if you let it install to default directory.
Now just right click and make a new folder and name it backup. It doesn't have to be named backup, it can be whatever you want. Now select all of it EXCEPT the custom folder and backup folder. Right click cut and paste all the OGG into the backup folder. At this point it should look like this.
That is all you have to do. Now you can play PSO at normal volume and hear NOTHING. Not even the warp into lobby/into game. All you will hear is the rare drop sound.
The best part of this, if you want to hear the music again, all you have to do is literally copy paste from backup to ogg folder and it's back to normal.
LAST TIP if there is some parts that annoy you or music you dont like, you can select which parts you dont want to hear, like the warping sound to lobby and put it in backup folder, it will not break or alter the game in any way and it will only not play that one specific sound.
If you have any questions feel free to ask and I will answer.
I feel like I should add this, if you want the custom music from the lobby that the GM's play, you have to take out the songs from the custom folder, but leave the rare drop sound as such.
Now if you get annoyed only by the lobby songs thats all you have to do, put the files (except rare sound) into a back up folder and they will no longer play.