The phenomenon you're describing, where fridges and freezers make creaking sounds at night when opening or closing the doors, can be attributed to a few factors related to temperature and humidity changes that occur throughout the day and night.
Temperature and Thermal Expansion: During the day, the ambient temperature is generally higher. When the temperature is higher, the materials that make up the fridge or freezer (such as metal, plastic, and rubber) also expand slightly. This expansion can help create a tighter seal around the door, making it easier to open and close smoothly.
Humidity: Humidity levels often fluctuate throughout the day and night. Higher humidity can make rubber gaskets and seals around the door more flexible and pliable. When the seals are more flexible, they can better accommodate the movement of the door without making much noise.
Nighttime Cooling: As the night progresses, temperatures tend to drop, and the materials in the fridge or freezer can contract slightly due to the cooler environment. This contraction can cause the rubber seals to stiffen and become less flexible.
Quiet Environment: At night, the ambient noise levels are generally lower compared to daytime when there might be more background noise from household activities or outside traffic. As a result, any minor creaking or noises that occur when opening or closing the fridge or freezer doors become more noticeable during the quiet of the night.
These factors together contribute to the perception that fridges and freezers doors work perfectly during the day but may make creaking or squeaking sounds at night. It's important to note that these noises are typically normal and don't necessarily indicate a problem with the appliance. However, if you notice unusually loud or persistent noises, it may be worth checking the condition of the door seals and hinges to ensure proper functioning and energy efficiency.