Why do mint-looking LPs sometimes play poorly?

I've purchased some older Japanese vinyl (e.g., pro-use LPs) and some older half-speed vinyl pressings (e.g., cbs mastersound) and on a few occasions, although they have *looked* perfect under very bright light, they play with quite a bit of surface noise. The LPs are not warped, and the surface noise persists after a thorough cleaning. Any insights or recommendations? Thanks!