> We speak of "noise" (interference)

Note that interference here has a very technical meaning that is NOT noise. (Sorry for the all-caps, but it's very important in these experiments.)

I think you don't understand the important point in the double slit experiment. Let's try to explain it, but it's a long explanation.

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First you must understand the single slit experiment. If the slit is thin enough you get a nice diffraction patter.

If this spread was caused by dust or something like that, a good guess is that the image gets a gaussian blur like exp(-x^2).

In a diffraction experiment, the image you get is something like sin²(x)/x². (You should draw them in Wolfram Alpha or something.)

The main difference is that the first one is always positive, so you get light everywhere, but it get's dimmer very soon. The second one has a lot of zeros, so you get strips of light and darkness. The math details are complicated, so let's ignore them.

You can do this experimentally. In the lab we used two razorblades with some screws to move them arcuately. There should be plenty of recipes in Internet to reproduce it. You can try it in more dusty environments, and clean environment. Sharp razorblades, not sharp razorblades. Wind or not wind. Try it a few times until you get use to the images it produces. You will notice that the cleaner environment produce the better results, so I hope you will get convinced that it's not caused by the dust or something

You can probably buy some single slit from an educational provider. Buy some of them of different width to compare the results with your homemade version.

It's important to understand how it looks before going to the second step, so play for some time with the single slit version. Some resources: https://en.wikipedia.org/wiki/Diffraction#Single-slit_diffra...

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Now, the double slit version looks more difficult to make at home. I think you should buy one (or a few), and the single slit version with the same width.

The idea is that if it has only one slit you would see the old image. If you have only the other slit you would see the old image. If the screen is far away and the slits are very close, you can't notice the difference. So you would expect to see the same image, but with more bright.

The weird thing is that you don't get the same image. You get almost the same image but with a lot of additional strips. There are the old dark lines and many new dark lines. These new dark lines are the interesting one. In this lines you have something like

. light + light = darkness

Try the experiment in air and try to read the explanations in https://en.wikipedia.org/wiki/Double-slit_experiment and https://www.youtube.com/watch?v=Iuv6hY6zsd0 . Try again until you scream <all-caps> "The new dark lines are weird!"</all-caps> If you are not screaming, try the experiments with one and two slits again and the info again.

You can try with a dusty windy environment, and it should make the lines more fuzzy. You can try wit a clean environment and get better results. The lines are not caused by the dust, they are just weird.

. light + light = darkness

(If you are going to buy things, add a diffraction gratting. It's like using many slits instead of two. The math is more difficult but they create nice rainbows. https://en.wikipedia.org/wiki/Diffraction_grating )

The dark lines are not so surprising when you use light that is usually approximated a wave. But if you get more advanced equipment you can repeat the same experiment with electrons or neutrons and get the same weird lines. (When you understand this, you can scream again.)