Q: How to determine plumbing layout inside floor/walls?

I have some pipes that I believe can use some insulating or sound proofing. Before I start a project that I can't finish, I need to find out the layout of the plumbing hidden inside the floor and some walls. I'm willing to cut and patch a small number of (small) holes to evaluate the feasibility of the project, but not more than that. What is the best way to find out how pipes (and perhaps cables too) are run when they're behind drywalls?
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All Thumbs wrote:

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