The elastic constant ${C}_{\mathrm{T}}$ and ultrasonic attenuation ${\ensuremath{\alpha}}_{\mathrm{s}}$ for ${(C}_{11}\ensuremath{-}{C}_{12})/2$ have been measured on ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ with ${T}_{\mathrm{c}}^{*}=1.42\mathrm{K}.$ In contrast to the ${A}_{1\mathrm{g}}$ and ${E}_{\mathrm{g}}$ strains, the ${B}_{1\mathrm{g}}$ strain $({\ensuremath{\epsilon}}_{\mathrm{xx}}\ensuremath{-}{\ensuremath{\epsilon}}_{\mathrm{yy}})$ strongly couples to the superconducting state, which dominantly originate from hybridized $\mathrm{Ru}\ensuremath{-}{4d}_{\mathrm{xy}}$ electrons on the $\ensuremath{\gamma}$ Fermi surface. Taken into account impurity induced in-gap states, the ${T}^{3}$ dependence of ${\ensuremath{\alpha}}_{\mathrm{s}}$ is found to be consistent with an existence of line nodes. The large reduction in ${C}_{\mathrm{T}}$ below ${T}_{\mathrm{c}}^{*}$ evidences the two-component order parameter and chiral p-wave state. Anomalous ${C}_{\mathrm{T}}$ and ${\ensuremath{\alpha}}_{\mathrm{s}}$ around ${T}_{\mathrm{a}}=1.34\mathrm{K}$ suggest a collective mode.