Lonestar Special has become noisy coming out of standby.

I have a Lonestar Special which has just started to make noises when the standby is switched out to start playing.
It is like waves of white noise ( like the sea rolling in ) and some squealing too. Then after about 5 to 10 minutes it is all back to normal and plays absolutely fine.
It is not channel dependent, and switching the FX loop in/out makes no difference. No controls affect the noise, reverb included. This only happens coming out of standby.
I changed all the tubes and the problem persists.

Any ideas ?

Thanks

Joe

Puzzling. The squealing sounds like a bad tube, not sure about the white noise though.
I'll assume you've unplugged everything but speaker and guitar and are still having the problem?
(Whether the loop is engaged or not, I'd definitely remove any pedals, tuners, etc. from the signal chain—both in front of the amp and in the loop—and test it that way to be sure. You never know. I've thought I had an amp issue in the past only to realize a faulty pedal or power strip was to blame, so I speak from experience. But hopefully you're smarter than I am. )

Also, make sure you've tried it with different guitars and different patch cords. Again, you never know.

Additionally, before you give up and call your local tech or Mesa, you may want to invest in a full re-tube (power and pre-amp tubes) using only new Mesa tubes. I know folks hate hearing that, since they are a bit more expensive and we all love trying different tube flavors, but the one nice thing about using Mesa across the board is that Mesa has tested them and vouches for their reliability in Mesa amps. The LSS can be finicky with certain brands of tubes in certain positions (look around for threads on tube issues in cathode follower, PI position, etc and you'll see what I mean), so sticking with Mesa tubes could help you determine if it's simply a tube issue before you go to the trouble of lugging it to your repair shop or shipping it off to Mesa.

But if you've eliminated tube issue and all possible external issues, then I'm afraid I'm out of ideas. Hope you get it sorted out. Let us know how it goes.

Thanks for the advice. Much appreciated. I'll investigate further this weekend when I can get it off the truck and back home.
The noises were happening with no input at all ie not even a guitar cable plugged in. I also carried it to the back of the hall and plugged it into a different power outlet - the one the sound desk was running off.
As a quick attempt to fix it, I put all the original working tubes back in ( they were left over from a re-tube I did a few months ago ). That didn't cure the problem. Once I get the amp home I'll investigate whether there is a tube socket problem somewhere, since I couldn't find an actual bad tube.
I'll post again when there is further news

Joe