I was jamming with my buddy nick, who's got a mesa Roadster, and I was ugin my 5150II, through a Peavey MS412 with Celestion G12t-85s, and when I crank the gain, I get a uncomfortably loud buzz through my speakers. It's not louder than the amp, not by a long shot, but something is obviously going on, unless the 5150II is just a buzzy amp. The buzz goes away when I flip off the standby switch, but not when I activate the mute on my tuning pedal. Conversely, Nick's Mesa was dead quiet at all gain levels when he was muting his strings.
The tubes in this thing might be stock, they're not labelled, as far as I can see, and I've never changed them, though I've only been owning it for 3 months at this point. Will older power tubes generate noise like this, indicative of them needing to be replaced?
What else could be going on here, and how will I fix it?
Plug just the guitar into the amp, skipping everything else. If it still buzzes, try a different guitar and cable. If it still buzzes, try replacing the preamp tubes first, and the power tubes second.
If it stops buzzing when you go guitar straight in, then you know the culprit is in your signal chain.