Popping/fuzz sound when I turn my amp on?

[mercilessdeath86]

Probably something obvious that I'm missing but when I switch my 6100LM to standby and then switch it back it makes sore of a popping and fizzing noise? I can't really explain it. It only lasts for about a second. Is this normal? I think I must have something switched to the wrong setting on the back panel.. Anyway please tell me my amp isn't fucked.

 

[MG100]

Valve nearing its end of life?

 

[mercilessdeath86]

Are there any other telltale signs besides that? They're bright orange when they're fired up