Thanks for all the replies so far, folks. I had a new idea about this flat tire business. Read on if you dare.

The tubes are two years old. Does latex age and go bad? Surely, it does, don't you agree? Perhaps what happened was either embrittlement and/or decomposition with age.

Our latex rubber brake hoods go south in a big way with time. They happen to be very thick, I'm guessing but let's say about 1/8" to 1/4" thick.

The tubes are very much thinner than that and are being subjected to fairly high pressure and stress due to inflation and vibration from riding. Maybe that thin wall cannot hold off the aging process more than a couple of years and then you get the bang or hiss.

A weak rim tape doesn't help.

Sticking to the insides of the tire doesn't help, either. I wonder if the adhesion is the result of the decomposing rubber, which as you know, is very sticky (think brake hoods here).

It's just a thought.