Recently, when I have been turning on my amplifier, a Marshall tsl100, for the first 20 seconds or so there is a static-like noise coming from the amp. What could this be? I am almost certain it is not the tubes as I did a full retube a few weeks ago and they have less than 3 hours of play time on them. Should I worry about this, and if so, how can I fix it?
mayhap a cap going bad. i wouldn't really worry about it too much unless the problem starts getting worse (but problems like that tend to get worse).
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
Anything through the effects loop?
Do you turn straight on or leave on standby first? If the latter how long for?
What condition are your leads in?
Is it a combo or hear? If the latter are you using speaker or instrument cable and to what cab?

A few things to consider in addition to the questions above - gives us a far better chance of figuring out possible contingencies...
It's an opinion. It's subjective. And I'm right, anyway.
Nothing is in the effects loop, I warm it up for two minutes, leads are in good condition, it is a head going into a Marshall 1960 lead cab.
Take it to a reputable tech - sounds like a cap... If the noise is in anyway microphonic there could be a tube problem. It should only need about 30 seconds to get to operating temperature. There may be a dry solder joint in there, something not entirely unheard of in Marshall's.
It's an opinion. It's subjective. And I'm right, anyway.
Sorry for bumping this thread as it is a few days old, but I thought it would be better than starting a new one on the same subject. It only happens when I have the VPR(virtual power reduction) engaged. If you are not familiar with the amplifier, this brings it from 100 watts to 25 watts.