[W9TR]

If I read correctly, you’ve tried the Puritan xxx-DC and it didn’t make a difference, correct? If that’s true, I’d expect the Emotiva CMX-2 or any other DC blocker wouldn’t work either.

That leaves the toroidal transformers in the amp themselves. Most of these multichannel amps use toroidal transformers because of their small size and low cost. IDK anything about this outlaw amp, but let’s assume what I’ve hypothesized is correct. It has two big toroidal power transformers.

The width of these amps has to be 17” to fit in a 19” rack, so I’m guessing the transformers are mounted to the front panel somehow. If that’s true….

You’ll have to take the amp apart and physically isolate the transformers from the front panel with some vibration isolating/absorbing sheet stock, like Sorbothane. You’ll also have to change out any metal washers with nylon, add sorbothane to the back of these washers, etc. You get the picture. Isolate the acoustic noise source

You could also increase the mass and damping of the front panel by adding a sheet of Dynamat or something similar to the outside. For appearance sake, if there is room on the inside (doubtful) you could add Dynamat to the inside of the panel before you add the Sorbothane.

https://www.sorbothane.com/sorbothane-sheet-stock.aspx