Tonight I was playing guitar, and when I stopped playing, I noticed a fuzzy kind of hissing sound coming from my Peavey XXX. Its coming from the speaker only when its on the distortion channel. Im thinking its the onboard distortion too because I plugged my TS9 in and had it on full on the clean channel with the volume all the way up and it didnt do it. The power tubes are glowing normal, and I cant check the preamp tubes as easily because they have metal shields over them. What Im wondering is if my amp is safe to run because of that noise, or should I try to get a pros opinion on it? If I did that, it would take a lot of effort as the nearest amp tech is a 50 mile drive away, so if its not immediately hurting my amp right now, I'm not going to worry about it unless it gets worse, but if anyone knows what this is or if they've had this problem before, please just tell me what you think it is. Thanks, and sorry for the rambling rant, Im half asleep
Try a different outlet in your home first. Distortion picks up on white noise throughout the house more than a clean channel.

If that doesn't work, try the amp on like a spongy or middle setting in comparsion to the bold setting. Bold pushes the tubes harder, therefore, their longevity is cut short.

If neither solves the problem, cut the amp on standby, then off, cut it back on (standby first). Do this a few times. If that solves the problem, then don't worry about it. If the problem persists, or happens a few days later it is a preamp tube problem. Whenever there is a problem with a specific channel, you lose a load of gain, or the amp will not cut on at all, 99% of the time it's a preamp tube problem. Power tubes are easier to identify the problems, they'll either be glowing much brighter, or your tone is going to be quieter and weaker.
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is it doing it even with the guitar volume off? If so, it's probably a preamp tube going microphonic.
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Crap, Im really hoping its not a microphonic tube. I got one replaced that was so microphonic I couldnt hear anything, and there was a loud high pitched ringing whenever I turned off standby. Im at school now, so I cant check the standby on and off thing, but Ill try it when I get home. If anyone else has any opinions, let me know. Thanks.
Check to see if you've got a loose tube. Otherwise, it sounds to me like you've got a tube going bad. MESAExplorer had a good way to go about it.