I have a Specialized Crosstour that is about 10 years old. I rode it occasionally and never had a flat. Then it hung in my garage for a couple of years. When I took it down, the tires were flat and I couldn't shift.
It went for a tune-up. Hours after getting it back, the front tire went flat. There was a single small hole, so I applied a patch. After sitting overnight, it was flat again. The new hole was 2 inches from the previous.
I tried patching it again. Before patching, I inspected the tube & tire. I couldn't see anything and didn't feel anything sharp.
The second patch went flat, so I took it apart, and wiped down the rim, rim strip, and inside of the tire. Never did I feel anything sharp.
I installed a new tube this time. This held for about 3 days, and then was flat again (I never rode the bike this time). This time the hole was on the opposite side of the wheel as the previous holes.
In all cases, it was a single hole on the spoke side and I aired the tires to 95 lbs.
My only guess right now, is that I am causing the flat by pinching the tube when putting the tube in. I air the tube up a little so it is round and am pretty careful when I put it in the tire.
I'm not sure what to do next and what could explain the punctures?
I came home on Tuesday, and my wife had taken it to the bike shop to be repaired. They didn't find anything and their new tube is still holding fine (3 days later).
I'm forced to conclude that I was causing the hole by my poor installation technique.
Update 2 The new tube install from the bike shop held for 3 days at about 30psi. At least it was at 30psi before I aired them up to 95psi and rode 2 blocks on our street.
The next day, the front tire was flat again. I haven't yet taken it apart to see where the hole is.
I accepted Popup's answer because it seemed the most likely explanation. I have replaced the rim tape with cloth tape AND used a thorn resistant tube. I will do the same to the rear when I have an issue with the rear tire or tube.