I don’t see why they would ever put pipes under slab in the first place. Then again, I know nothing about construction. It just makes sense to me to have pipes that will not break or shift, and if they do leak they are accessible for repairs.
In order to achieve this I’d put pipes in between walls with foam or fiber to insulate the noise. I would also put the hot water heater inside the house, it doesn’t make sense to me that they’d have it outside in the cold. I would also put it as high as possible, like in the attic. Let gravity bring the hot water to you. Of course it would require extra precautions in case of leak or rupture. Wouldn’t want a flood coming out of the attic.
