HUD objects are randomly unable to play sound dependent upon the attachment point and the location of the avatar. For example in area A with object in top left sound may not play whilst in area B sound does play, and that in area A with object in top right sound does play whilst in area B sound does not play. Issue has been spotted several times in this forums post: http://forums.secondlife.com/showthread.php?p=1538690#post1538690 This together with the other bug regarding HUD sounds not playing completely dependently on location makes playing sounds from HUD extremely unreliable.