I have a duplex and when the upstairs apartment turns on the hot water I hear a LOUD ticking/banging noise in my basement (2 floors down). A plumber told me it's the copper expanding and hitting the pipe clips and that I have to loosen the clips…..
I have located on approximately which wall the noise is concentrated….But it could be on either or both of my floors…
How do I find out where the clips are too tight without ripping down two full walls (upstairs and downstairs)??

Check with your local building department to see if they still have your blue prints.

Unless you have a set of prints, there is no way to tell where the straps may be too tight.

Try a stethoscope on the wall. Unfortunately you will have to wait around until to other resident uses hot water. Who owns the building?