I bought a texture from gametextures.com (Download option “PBR-Metallic”), but it’s not looking right. There are spots that keep appearing and disappearing and there are some unnatural looking, aliased white line highlights. I just created a material and assigned all the textures. Is there something else I need to do to make them look right in Unity (2017.1)? I tried switching some things around but to no avail.
https://www.gametextures.com/gametextures-to-metalness-a-new-tool-to-convert-workflows/
Unity 5 and Unreal Engine 4 both use a metalness / metallic workflow, but they use very different texture layouts. I suspect the textures you downloaded are not setup for Unity 5 (and might not even be setup for Unreal Engine 4 either) and need another manual step to convert them to the proper layout. The link above should have the tools that will let you do that, but I’ve not used them so I can’t really help or comment on them.
I can say the Unity 5 layout for the standard shader is thus:
Albedo texture = RGB Albedo color, A Optionally Smoothness (if not on metallic)
Metallic texture = R Metallic, A Smoothness (inverted roughness)
Normal Map texture = RGB Normals
Emission texture = RGB Emissive color
Height Map texture = G Height
Occlusion texture = G Ambient Occlusion