Noise on the viewfinder (monitor) becomes more noticeable when the shutter button is pressed halfway down.

Noise becomes more noticeable when you press the shutter button halfway down while using a narrow aperture in the A mode with Anti-flicker Shoot. set to On.

[1] Before pressing the shutter button halfway down
[2] When pressing the shutter button halfway down

This symptom occurs because the frame rate of the live view becomes faster in order to detect flicker.
The shutter speed of the live view also becomes faster in accordance with the frame rate, and the amount of light decreases.
The noise increases to compensate for the lack of luminance.

This noise does not affect the actual recorded image. However, if you are bothered by it, turn off Anti-flicker Shoot..