Try to swap tubes (with the power Off) - one at a time from left side to right, and see if the problem switches also, when it does - you found the problem.
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The woofers flapping is due to an infrasonic oscillation, possibly due to a small-signal tube. The first thing you need to do is power up only the power amp . If the woofers flap, try swapping the input/ driver tubes from one channel to the other (or use a new tube, if both channels use half of the tube). You should NOT have to wait an hour, either--wait a minute or two, and use a potholder to grab the hot little tube. Don't bother worrying about the output tubes--I've never seen them cause an infrasonic oscillation.
If they don't flap, turn off the power amp, wait about a minute, then turn on the preamp and, after it's warmed up for a few minutes, turn on the power amp. If the woofers now flap, swap the tubes in the preamp.
If they didn't flap at all, it's either your CDP, or the problem has disappeared (but it WILL be back sooner or later). BTW, I've been an electronic technician for 30+ years, and have manufactured a tube power amp.
DC belongs on every tube plate except a rectifier tube. If you don't know the answer, don't make one up.
Sorry for not posting this earlier!
It turned out to be the set of small tubes on my amp!
I'm not sure if they are input tubes? or what they are called...anyway, I took the amp to the dealer, they gave me a full diagnostic eval on the amp and preamp that I brought and told me that one of the tubes had simply gone bad!
They gave me a new tube for about 15$, gave me a tour of their factory!
Thanks very much to the staff at Rogue! Very helpful and SUPER friendly!