Phonon softening and slowing-down of charge density wave fluctuations in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">BaNi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">As</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

BaNi$_2$As$_2$ is a nonmagnetic analogue of the iron pnictide superconductors, and in its tetragonal state exhibits an incommensurate charge-density-wave (IC-CDW) sizable elastoresistance. In this work, phonons associated with IC-CDW uniform in-plane lattice distortions are investigated using high-resolution inelastic X-ray scattering. The transverse acoustic reveal no softening at temperatures where elastoresistance increases strongly, indicating latter to be electronically driven. Systematic phonon measurements occurs two stages upon cooling: underdamped first soften zero energy well above ordering temperature, then resulting quasielastic fluctuations gradually slow down coalesce into static order. A possible origin for our observations being uniaxial, which provides additional Ising degree freedom favorable disordered modulations, accounts through weak coupling lattice.