We plan to measure the phonon dispersions of the rare earth pyrochlores Tb2Ti2O7 and Ho2Ti2O7 in their spin liquid and spin ice phases respectively. Magnetoelastic effects are strong in Tb2Ti2O7, where they seem to stabilize the spin liquid phase against either structural distortion or spin ordering. Meanwhile, an Orbach process is thought to control monopole hopping at high temperatures in spin ice. We will compare the phonon dispersions and crystal field excitations of the two compounds with each other, and DFT calculations. In this way, we hope to identify completely the magnetoelastic interactions of Tb2Ti2O7, and to understand the ``simplest'' monopole hopping mechanism in a spin ice.