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A three-dimensional compound series (Ca_xSr_1-x)₃Rh₄Sn₁₃ has been identified as a promising system to understand the interplay between charge-density-waves (CDW) and superconductivity. The second order CDW transition temperature T^* in this family can be fully suppressed with the substitution of Ca for Sr, giving rise to a Quantum Critical Point at x≈0.9 at ambient pressure. For a comprehensive understanding of the lattice instability connected to this CDW transition and superconductivity, diffuse scattering measurements were performed on single crystals of (Ca_xSr_1-x)₃Rh₄Sn₁₃ with (x=0, 0.1, 0.5, 0.6, 0.65, 0.7, 0.9) using x-ray diffraction. A 3D-ΔPDF analysis shows that there is an order-disorder transition at T^*, with local distortions still present at higher temperature.