Open your browser to the flash application, locate the mute button sound. Sometimes the buttons can be two – one of them disables the music, if any, in your case, the other mutes the application itself. If you can't find them in the control menu, read the information carefully to users about its use; perhaps there you will find options to disable sound.
Go to the main settings menu of the flash application; it is possible that sound and music can be adjusted or removed entirely in one of its paragraphs. Also try to click right mouse button directly on the program itself and find in the context menu of the desired option.
If you want to disable sound in the flash app that runs on your computer, use the special software to open them. They usually contain additional playback functions, which imply also the possibility to disable sound or music. You can't use conventional browsers, you probably need flash player.
In cases when you need to turn off the sound, you can use the full mute the computer. This is true in cases where the program menu does not provide for special control or you simply can't find it.
This can be done by pressing the corresponding button on your keyboard, reducing the volume level to the minimum in the speakers or headphones, including the minimum volume level for sound card from the appropriate menu in the lower right corner of the Windows taskbar and so on. This method is not convenient because it will also affect playback of your music player, video player, chat programs online and so on.