After a random amount of gameplay time, my skill sounds begin to cut off, while still being able to hear party member's skills and bgm, and after a few more minutes, the only thing I can hear is bgm. Opening buddy list, inventory, stats, etc. will have a portion of the window cut off as well. Sometimes the screen will go black but the client itself is not frozen.
this is common, we called it gfx. it usually happen before raid, during raid and after raid. re-client or restart computer will help.