The pyrochlores provide an excellent model system for studying the interaction of framework vibrational modes, defects and magnetism. We propose to investigate these couplings with a comparative study of phonons in non-magnetic Y2Ti2O7 and La2Zr2O7 (for which we already have data) and the frustrated magnet Yb2Ti2O7, for which we request experimental time on MERLIN. The results will be compared directly with our calculations using density-functional theory, which are challenging due to the presence of large, disordered magnetic moments. By comparing our results with mass substitutions we can assess the extent of electron-phonon interaction, and potentially explain why the oxygen vacancies in Y2Ti2O7 and Yb2Ti2O7 are different. We shall also assess whether static displacements recently reported for Yb2Ti2O7 are really dynamic.