System start-up noise

Happy Super Bowl Sunday,

I have a question about what may be causing some noise my system is producing just after start-up. Please note that all the components involved are always in stand-by. The components involved are a Sonic Frontiers Line 1 preamp, and Parasound JC1 mono amps. The speakers are Triangle Volante 260.I always bring the preamp out of stand-by first, it has a thirty second mute process while powering up. Then I bring the Parasounds out of stand-by, while the Line 1 is in the mute phase.  If I don’t put any music on, I’ll hear a muffled distortion-like noise from one or both channels after about 3-5 minutes of the system sitting idle. The  noise isn’t loud, and has an intermittent quality.  The first time I noticed it I wasn’t paying attention to the stereo, and at first thought a squirrel had gotten into the eaves and was scurrying about.  The noise had that quality of muffled scratchiness. After a few minutes, the noise goes away, and doesn’t return until the next time I bring the system out of stand-by.  I’ve never heard the noise while playing music. The Line 1 has has three pairs of 6922 tubes, could these be the cause?  I bought the unit used, and I have no idea how old the tubes are. 

Thanks in advance for any advice, 
It could be dirty 6922 tube pin/tube socket contacts in the Line One preamp.
Usually just pulling the tube/s out of the socket and reinstalling it repeatedly a few times will clean the tube pins and tube socket. You can also use rubbing alcohol sparingly on a q tip to clean the tube pins. Even then I would still install the tube, pull it out, and and install it repeatedly a few times to clean the tube socket contacts.

Please note that all the components involved are always in stand-by. The components involved are a Sonic Frontiers Line 1 preamp, and Parasound JC1 mono amps.
Why do you leave the Line One preamp in standby 24/7? Even in standby you are shortening the life of the tubes. The tube filaments are still energized.


Some tube equipment companies’, "Standby" practices, keep the gear at half voltage and zero B+.      That avoids thermal shock, at turn on.      Sonic Frontiers doesn’t mention the half voltage thing.      Still; keeping the filaments energized, is supposed to better for the tubes(etc), than a cold start.      Not to mention: warm up, as regards presentation.      You may have a tube, with an internal glitch, which corrects after fully heating.      If the noise only occurs in one channel, try swapping the tubes between channels, one pair at a time, to locate the offender. If in both channels; there’s probably another issue.      I’ve always given my tube gear a few minutes(each piece) to stabilize, before bringing anything else online.
Perhaps I should have mentioned(regarding that last sentence): still following the standard, source-through-power-amp, turn on sequence.      And- I’d be disposed toward cleaning the tube pins & sockets, first(as advised).       Should that have been, "on line"?
I've heard that sound many times and it's almost always noisy tubes that stabilize when heated up. 
I agree with the above that it is a noisy tube. You can pull the tubes clean the pins with 4-0 steel wool and try them again. If the preamp is over  years old I would consider replacing them. The super low noise 6922 from here are the best you can buy. I use them in my ARC phone preamp (which I leave on all the time) They are at least 10 dB quieter than the tubes ARC used.