Bicycle Mechanics - Pinhole Leak in Tube

I found my bike today with a flat rear tire. I took the tube out of the tire and inspected it, and after putting it under water, I found a tiny pinhole where the leak was. It is on the rim side of the tube, about where the tube would contact the bead of the tire.

I've heard of people getting tiny wires separating from the tire and causing such problems, but I'm using a foldable tire, not a wire-bead, so I can't see that this would be the problem. I've ran a cloth around the inside of the tire and the rim multiple times, and haven't snagged anything on either, and I've run my fingers over both to make sure that there wasn't something really small there.

The only thing I found was that the rubber along the very edge of the bead is pretty rough in a couple of places. Has anyone ever heard of, or had experience with, that causing a leak, or is it more likely that I just picked up something from the trail that I brushed away when I was checking for it?

cineris: Try running a cotton ball around the suspect area. It also might help to turn the tire inside-out when checking for embedded objects.

Wire

http://i256.photobucket.com/albums/hh187/10wheels/Tire%20Repairs/Royswire.jpg

Glass

http://i256.photobucket.com/albums/hh187/10wheels/Tire%20Repairs/RoyswireNoGlass.jpg

The tube may have been slightly twisted so that the part where you found the hole was aligned with the tread rather than the bead. In any case, the pix above show things like I've found in my tires, sometimes even smaller. In fact yesterday I got a slow leak during a ride, stopped, removed the tube, could not find the hole in it, carefully inspected the tire, found nothing, put a new tube in, and rode on only to get another slow leak. I made it home and was able to find the leak in the tube and then look at the corresponding place in the tire. I found I nearly microscopic flake a glass embedded in the tire. I had a similar experinece about 6 months ago caused by two very thin pieces of wire embedded in the tire about 180 degrees apart. I found the one corresponding to a leak and removed it only to get another slow leak a few days later caused by the second piece of wire.

I had a batch of tubes (I think I ordered two or three from the same place, same time) all have pinhole leaks. I could find no culprit, and no tubes before or after have ever had that problem.

I found a tiny pinhole where the leak was. It is on the rim side of the tube, about where the tube would contact the bead of the tire.

bead wire exposed?
Bad tube is always possible..

bead wire exposed?
Bad tube is always possible..

I've had one of those. There's just nothing you can do to fix an exposed bead wire, except getting a new one.