Rear 700C tire on hybrid bike flat/deflating seemingly at random I have a hybrid bike and I am having a very strange problem with deflating tires.
My bike has 700C 35/43 tubes
I have changed 3 tubes in the last 2 weeks because something very strange is happening.
Tube 0

That I had for a long time punctured
I found the small hole

Tube 1

I change the tube and pump it to the suggested pressure of 80-85psi.
I ride it for 1 day, check the pressure, it stays at 80-85
I leave it overnight, check the pressure, ride it for 1 more day, check the pressure, everything is fine
I leave it overnight, the tire is completely flat. I

Tube 2

I change the tube and pump it to the suggested pressure of 80-85psi.
I ride it for 1 day, check the pressure, it stays at 80-85
I leave it overnight, check the pressure all is fine, ride it to the supermarket, pressure is fine. Go in for 1-2 hours, come out, tire is flat.
I pump up the tire, ride home, check the pressure, everything is fine.
I leave it overnight, check the pressure in the morning, everything is fine.
ride to the office, check the pressure, everything is fine.
come out for lunch 3 hours later: tire is flat.

Repeat with one more change of tube. Same result. Completely random deflation.  I visually and tactilely inspected  the rim, the tire, the tape and cannot find any problem. The tire is not new, sure, but it is not bald either. Should I replace the tire? The whole rim/wheel (more expensive, also, the cassette is difficult to remove and I have never done it)? The whole wheel with cassette? The whole bike?
I am somewhat technically minded so I tried to understand but my observations essentially are useless as I can find no logical pattern. Has anyone had any similar experience?
Thanks!
Something subtle is in the tyre puncturing the tubes. It may be rubbing rather than piercing, and it may be imperceptible without pressure, but it's there. To help you locate it, align the logo on the tyre with the valve every time. Then when you find the hole in the tube you know where to look in the tyre (with some margin for error, and you might flip the tube over, so check the other side of the valve too).
As well as glass, wire, screws etc. I've had the threads from a nearly worn out tyre appear on the inside and cause slow punctures, and I've had the inner end of ice spikes wear holes in tubes.
Slow punctures are odd. They can seem to hold for a while then drop suddenly. Whether that's real or just that you notice suddenly, I don't know, but I've had a couple recently do odd things like that