I had assumed that if anyone could have gotten rid of the noise without otherwise changing the character of the sound by pushing in a button on analog gear, the button would stay pushed in.
But there used to be (still is, in some cases) noise from the desk, the outboard and tape. In the digital domain, you have none of that -- the noise floor is zero.
Here's an explanation of noise in Waves plugins. The 'intermodulation' aspect is something I don't recall having heard:
Simon A. Billington: On the H-Series it sets the different type of analogue emulation.
In the API it’s tied to both the noise and the harmonic “character”
In other plugins it simply controls Noise and Hum. Which I don’t usually mind a little bit of myself. It interjects a bit of intermodulation which helps achieve a more cohesive mix.