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It's hard to say without seeing the .blend file, but keep in mind that if you're using metal or plastic materials, even some procedural ones, that you downloaded or found in a repository then there's a chance it contains tileable image maps as part of the material somewhere in the node structure. If you created the materials yourself from scratch, and you know for sure they are completely procedural, make sure there weren't any addons involved that some people may not have. Another area to check is background images.
I made it myself, a basic material of metal and plastic. It has no texture applied because it doesn't need to. Only the PBR material without any nodes applied to it.
