How does repeatetly moving food from freezer to fridge and back every day affect it?

I assume you have no food that needs to be kept frozen. If you do that's your greatest concern.

If, as suggested by your measurements, the fresh food never gets above the recommended maximum fridge temperature, the quality is going to suffer, possibly quite a lot, but the safety shouldn't, within the use by dates.

You may be able to keep the quality better by leaving the food in the fridge, but transferring a lot of ice from the freezer. I'd freeze several large plastic bottles, about 3/4 full of water, when the freezer is running, and move those into the fridge when you turn it off, leaving the food in there. Refreeze the next day. This is the approach used in many camping coolers, and it sounds like you have the ability to ensure the temperature doesn't get too high.

If it's so noisy that it's keeping you awake through earplugs, even if it's right next to your bed, that is quite likely to mean it's on its way to failing completely. The fact that your freezer is warming so fast is probably partly the unfrozen food going in and partly that it's empty of frozen stuff. It may also be a further sign of imminent failure.

Is it the fan ?

You are stating that the freezer is at about 3-4 C that is within the safe zone for refrigerated food. And the actual food having been colder and warming up may actually be slightly lower than the air temperature in the freezer.

Fans are usually fairly quiet on a recent models of fridge freezer.

If a fridge freezer is loud enough to keep me awake when wearing earplugs it must be fairly noisy, and I would be thinking it is likely to be a gas leak or compressor fault. That may result in a fridge freezer not being able to attain safe operating temperatures.

However you have stated that in a follow up comment that you do not keep frozen food. So there are no concerns about that being affected by the repeated turning off of the freezer.

At present the food is not likely to be detrimental to health, but if it is a progressive leak or compressor failure the may not remain so in future.

A couple of links:

• Noisy Compressor
• Noise and Other Problems

  • Sometimes a freezer can get noisy simply because it is not installed on a level surface. Ensure that it is placed on a flat surface before testing for other issues. This noise may also be caused if the Defrost Water Pan is loose or has not been properly installed. Other common issues that lead to this type of problem are malfunctions in the evaporator motor, condenser motor, or the internal compressor.

The tendency to get ice crystals in fresh refrigerated food suggests it is actually below 0 degrees C. That is affecting the texture and quality of the food but not producing a health hazard.