Ultrasonic noise should have no sound to it. It is, after all, "ultra" sonic which means it is beyond our hearing.
Yet, we know removing ultrasonic noise riding on the music reduces glare and brightness. So, if we cannot hear noise how does it add to the brightness of sound?
Here's my unscientific guess as to why that's happening. High-frequency hash and noise upset the amplifier's circuitry and that's adding a degree of harshness.
We know from years of experience in circuit design that feedback circuits struggle when challenged with higher-order frequencies. Circuits without feedback sound much more open and are more tolerant of square waves and other high-frequency events that can trigger ringing. (One might then ask why anyone would bother with feedback at any level and that's a discussion for another day. Let's just suggest engineering is all about the best compromises for a given result).
The point of this post is simple. Cause and effect are not always 1:1. In other words, it would be easy to argue the logic that ultrasonic noise cannot be bright since we cannot hear the noise. Yet, our experience shows us something very different.
Just because it's logical doesn't make it right.
