So I bought a prusa i3 kit from a company called folger tech off of ebay. I've built it and even printed out a few parts, but I noticed that a lot of noise seemed to be happening only while the x-axis motor was moving the extruder. Then I noticed if I put my finger lightly on the plastic part of the x-carriage I could dampen the vibrations and pretty much eliminate the noise I noticed. Then I took apart that part of the printer and examined everything and all I could notice that seemed to be loose was that nut that allows the z motor to push up the x carriage. I don't know if I got a bad nut, or a bad screw, or is it's just supposed to be this way? I thought it was kind of a weird way to build things with a screw turning a nut, because I thought that it would bind up. But now I'm wondering if that is why it was so loose fitting (to reduce friction)? So does it need to be that way? Or could I get a different nut? Or is there some better way to go about fixing this issue? Or perhaps it's not even an issue.. idk.
It's probably intentional. Threaded rods are almost never perfectly straight. If the nut is rigidly coupled to the carriage, then the slightest deviation in the screw will either cause it to bind up or appear as artifacts (e.g. z-wobble) in the print. By making the nut slightly loose, it can move around a bit to compensate for wobble. See e.g. this design and this design for how this is commonly implemented in other printers.