Nope, it's not BS. Onkyo holds many patents for anti-vibration designs. Here is one:
https://patents.google.com/patent/US7773373Of note is the following excerpt:
"The function of the vibration-damping structure of the AV amplifier will now be described. With a configuration as described above, when the power of the AV amplifier is turned ON, a voltage is applied to the main transformer 52 and the sub-transformers 53 and a current flows therethrough. As a current flows through the main transformer 52 and the sub-transformers 53, these components vibrate slightly. Moreover, the exhaust fans 54 are rotated by a driving circuit (not shown) to also vibrate slightly. As the main transformer 52, the sub-transformers 53 and the exhaust fans 54 vibrate slightly, these vibrations are transmitted to the component accommodating chassis 45 on which these components are mounted.
Since the component accommodating chassis 45 is fastened to the sub-chassis 25 so as to be partially in contact with the sub-chassis 25 via a plurality of fastening members, the vibrations of the component accommodating chassis 45 are attenuated while being transmitted to the sub-chassis 25. Similarly, since the sub-chassis 25 is fastened to the main chassis 11 so as to be partially in contact with the main chassis 11 via a plurality of fastening members, the vibrations of the sub-chassis 25 are further attenuated while being transmitted to the main chassis 11."
There's more interesting reading below the above excerpt that describes the nasty effects of these vibrations on the audio signal.
Norimasa Kitagawa and the rest of his crew wouldn't make this up. These guys do nothing, I mean absolutely nothing in their lives but eat and breathe this stuff all day and all night.
P.S. I remember reading that Onkyo had a heck of a time with vibration modelling. They'd introduce stiffening in one area only to discover that reflections from the stiffener resulted in more complex vibrations that created more problems. This is one reason a well-designed EI transformer is preferred over a toroidal transformer for power supplies. The EI transformer is less likely to vibrate particularly with a DC component on the powerline.
