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, 

Showing 2 responses by rodman99999

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"?