Help! Sony TV -trinitron- sound problem!!?

I had this TV for awhile now (about 8 years or so- it served me well), but recently the sound failed on me...ahh i need help!!! when i turn on the TV & setting the TV volume to its highest level, i hear this high pitch in the background. After 3-6 mins, all sound is gone. Whats wrong?? anyone with any suggestion or website where i can research more about "sony/ sounds problems?" plzz i need your help!!! thank you!