I'm hoping my pics show up as I'm posting from a phone. I just noticed these cracks in the paint today after taking my rear wheel off for travel. They're not scratches from a tire. The wheels I've used in it are perfectly spaced, so the dropouts aren't being forced apart ever (what it looks like to me). I've never crashed or even dropped this bike. Any thoughts? Any seen this before and know what would cause it?

Everything is a stiff as ever and nothing creaks.

I bought the frame like new on here a couple years ago, so I'm sure no warranty since I'm not the original owner.