I was just sitting here in my cube, hours after my ride, and ssssss there goes my rear tire. WTF! I have it apart and found the leak. There was an obvious fold in the tube, I was sure it would be there, but it wasn't. It's on the rim side. This is a really strange cheap rim, looks double walled but instead has a very deep channel, but I can't find a jagged edge or protruding spoke or anything like that.