Cluster of stuck pixels

I have a Toshiba 20AF43 TV (standard flatscreen) that I purchased in late 2003, which was working great until recently. The screen has developed a 4x4 cluster of stuck pixels (maybe not the right word, because this is not an LCD) in the upper right hand corner of the screen. These pixels are located just below the channel number and label, and are the same bright turquoise color as the text. They remain stuck on even once the channel number and label have disappeared. However, if I mute the sound or go to the control menus the blue spot disappears and the picture displays normally (i.e. the pixels are not dead or burned-in). I have tried restoring the factory settings and clearing all the channel labels and changing the display settings in the menus, all to no avail. I can't seem to find any information in the manual on this problem. Thanks in advance for any advice you can offer.