Is it the negative speaker post on the amp?
Is it the negative speaker post on the speaker?
Is it the cable?
This should not be too hard to figure out. You have several components that can be the problem. If you isolate each component to verify it is OK, you will narrow things down until you are left with the problem.
Start with the speakers. Switch them from right to left. If the problem doesn't move with them, the speakers are OK.
Now, do the same exact thing with the speaker cables. Again, if the problem stays the same, you have now eliminated both the speaker and speaker cables.
**I just noticed something in your post. You don't say if the problem occurs with just one or both your sources. Unless you say otherwise, I will assume both and that will rule out all source components and cables. ****
Now go to the amp. I know you have tried new tubes. Try this anyway: Turn the amp off and move the tubes from the right channel to the left and from the left to the right---do all of them, not just the power tubes. If the problem follows the tubes, you have the problem.
Unplug your subwoofer and remove the IC. If the noise is still there, I would have to say that there is some type of internal issue in your amp. But first..
Completely disconnect 1 of your sources (TT, phono pre, interconnects and powercords or Transport, Dac, interconnects and power cords). If after completely disconnecting one of your sources the noise is still there, hook it all back up and unhook the other source.
If the noise is still there after checking both sources, my best guess would be something in your amp or your AC. If you can, try the amp in a different location. If the problem follows one of your sources, you should be good enough at this by now to keep going and isolate the problem.
Also, I'm not a repair person of any kind and could have very well overlooked something. Check all the other posts as they may have thought of something I missed.