Huge Marshall JCM200 TSL122 Tube Problem

Hi guys, I'm new to this forum, but plan on contributing my knowledge in the future to help others with similar problems, or anything else that I might be able to help with. Now, currently, amp has been making this crazy distorted noise that sounds extremely unbearable, and I managed to get a video of it.

http://youtube.com/watch?v=Pp9lUd7HVYo

If you watch, there is a crazy distorted noise that happens about halfway through, then, towards the end, one of my tubes produced this insane shock. I don't know what the problem is, or how to fix it, but any help would be greatly appreciated.

Thanks,

Paul