Originally Posted by DnvrFox

I would suspect a very, very tiny piece of steel wire hidden in the tire - from a steel belted radial. One that only shows if the tire is compressed against a filled to pressure tube. To find it, you are going to have to turn the tire inside out andgo through the entire tire pressing against the exterior - which will be inside, looking for a tiny piece of wire to show its ugly face.

You will keep buying tubes again and again until you find the cause.