Im trying to sculpt noise in zbrush, but i cant figure out how to make the brush paint ONLY noise. If i make Z intensity 0, the noise stops forming, and if its higher than 0, the brush also raises/lowers the surface of the mesh. (i dont want to raise/lower the surface, i just want the noise)

I'm a bit confused to be honest. Sculpting anything generally means raising or lowering the surface. No surface change, no noise.

If you didn't want to change the surface, you could try turning off zsub/add and just paint the noise with RGB. Or use one of the bump materials which would basically convert the polypaint into a bump map.

Otherwise you'd have two options for noise that both affect the surface. One is the NoiseMaker Plugin (a low strength will keep the surface from changing too much while adding the noise, and you can use masks to control it). The second is the Surface Noise brush Modifier. It uses similar settings to the noise maker plugin now, but the important thing to note is that it's a brush modifier. If you use it with the Standard brush, then the brush is going to act like a normal standard brush, just with noise added. So to prevent large changes to a surface, you could try it on the layer brush (perhaps with a morph target before sculpting), or on the noise brush (which shouldn't alter the form too much).

yeah but basically i want the noise to deform the mesh on a +-0 scale. Like basically it raises the surface as much as it does lower it.

example: if i took a flat plane, painted noise on it, and then brushed it over with a smoothing brush, it would become perfectly flat again.

See edit

As Cryrid said, noisemaker plus morph targets are what you should look at. You can even mix noise patterns and adjust intensity with the morph brush and multiple targets this way.