I've got a Peavey Triple XXX and when I turn it on there is some sort of hiss that sort of fades out. I'm hoping it isn't a grounding issue or something like that. I've been swapping out pre-amp tubes and nothing makes it go away. Any ideas?
When you say you have been swapping out preamp tubes, what exactly have you been swapping and how?
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^ it means he is swapping his existing preamp tubes around in order of position

V1 -> V2
V2 -> V3
V3 -> V1

as an example.

ticklemeTS - did you try a different power outlet or house maybe?

if there is still hissing after the swapping you could still have a microphonic tube.

do the pencil test or go ahead and get a preamp tube in there to test with.