The CMB is not literally making a noise, but it is referred to as "noise" because it is a form of radiation that is present throughout the universe and can be detected by instruments designed to measure it. This radiation is constantly present and cannot be turned off, similar to background noise in audio recordings.
The CMB is the residual radiation from the Big Bang, which is estimated to have occurred approximately 13.8 billion years ago. As the universe expanded and cooled, this radiation was left behind and is now present in the form of microwaves with a uniform temperature of about 2.7 Kelvin.
The CMB "noise" is considered one of the strongest pieces of evidence for the Big Bang theory. The uniformity and temperature of the CMB, as well as its isotropic nature (same in all directions), are consistent with the predictions of the Big Bang model. Additionally, the slight variations in the CMB temperature provide clues about the early universe and its evolution.
No, the CMB "noise" cannot be detected with the naked eye. It is present at a frequency of about 160.2 GHz, which is in the microwave region of the electromagnetic spectrum. This frequency is well above the range of visible light, making it impossible for the naked eye to detect.
Scientists use specialized instruments, such as telescopes and satellites, to detect and measure the CMB "noise". These instruments are designed to detect the faint microwaves from the CMB and create maps of its temperature and intensity. Through these measurements, scientists can gain insights into the early universe and its evolution.