Noise occurs when alpha mode is mask.

[canny]

Manipulating the transparency of a PBR material can result in noise.

Enable the PBR material.

Set Alpha to 1.

Change the Alpha mode to Mask.

Set Alpha Cutoff to 1.

Then it will look like this image.

https://gyazo.com/24322c4986b503c71718f699de732108

When you set Alpha to 0, the cutoff will be applied correctly and it will be transparent.

The same thing happens when you apply a texture to the base color.

https://secondlife.canny.io/admin/board/bug-reports/p/noise-occurs-when-alpha-mode-is-mask

[canny]

This issue has been linked to a Canny post: Noise occurs when alpha mode is mask. 🎉

[AtlasLinden]

Recording of noise in action: https://gyazo.com/9e5c5dbb94ab58c4203d2624eecad09a

[canny]

This issue has been linked to a Canny post: PBR Material produces flickering noise 🎉

[Dan-Linden]

Kristy Aurelia notes in https://feedback.secondlife.com/bug-reports/p/pbr-material-produces-flickering-noise :

This produces a noisy/flickery surface. This is likely due to floating point rounding errors in the shader.

glTF spec says about the material.alphaCutoff - "If the alpha value is greater than or equal to this value then it is rendered as fully opaque, otherwise, it is rendered as fully transparent"

So with both values being 1.0, it should be fully opaque.