Metal Harbor has one ring that's above the second pulley (that set of two pulleys where you have to somersault first to get to them). You can use the Bounce Bracelet to get up to it. Metal Harbor has a small amount of rings so it's generally easier to perfect Metal Harbor compared to most stages.
Not quite what we're referring to: http://forums.sonicretro.org/index.php?showtopic=29656 How convenient, there's a topic about this already.
You can get a perfect on Metal Harbour, though that may just apply to Battle/the HD release. http://www.youtube.com/watch?v=SOyKu_8JcmE EDIT: Probably doable on DC version too, since someone in the topic Dark Sonic pointed out mentioned the 75 hidden rings under the start were in the Hard Mode mission.
There are 75 rings hidden under the first ramp in hard mode? What the hell is that? One accessible ring is doable, but that's just ridiculous. Although, if this doesn't point to a previous version of Metal Harbor existing at one point (or they just really messed up), I don't know what to make of it.
