What causes noise in electronics, like my charging adapter? Can a noise change or appear as something ages?
Noise in electronics can be caused by a variety of factors, including electromagnetic interference (EMI), radio frequency interference (RFI), power supply issues, and even thermal noise. These factors can produce unwanted electrical signals that can interfere with the normal operation of electronic devices, resulting in degraded performance or malfunction.

EMI and RFI are particularly common sources of noise in electronics. EMI refers to unwanted electrical signals that are generated by nearby electronic devices, power lines, or other sources of electromagnetic radiation. RFI, on the other hand, refers specifically to unwanted electrical signals that are generated by radio frequency sources, such as wireless communication devices.

Power supply issues can also contribute to noise in electronics. For example, fluctuations in the input voltage to a device can result in unwanted electrical signals that can interfere with its operation. Additionally, poorly regulated power supplies can produce noisy output voltages that can impact the performance of connected devices.

Finally, thermal noise can also contribute to noise in electronics. This type of noise is caused by the random movement of electrons in a conductor, and is more pronounced at higher temperatures.

In terms of whether noise can change or appear as electronics age, the answer is yes. As electronic components age, they can become less reliable and more prone to generating unwanted electrical signals. Additionally, environmental factors, such as changes in temperature or exposure to moisture, can also impact the performance of electronic components over time. As a result, it is possible for noise to change or appear as electronics age, and this can have a negative impact on their overall performance and reliability.
I hear a buzzing sound coming from my charger, and I have had it for several years. That seems to match your description, so I think it has degraded over time. Is it dangerous to continue using it, or should I buy a replacement?
Based on the information provided, it is recommended that you replace the charger as a buzzing sound coming from it could indicate it has degraded over time and may be dangerous to continue using.

It is better to err on the side of caution and replace the charger to ensure safety.