Structural phase transitions in relaxor ferroelectric materials remain to be one of the most puzzling issues in solid-state physics. In the present work, we have investigated relaxational and vibrational properties of a relaxor ferroelectric 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 single crystal by means of inelastic light scattering measurements. Analysis based on the spectra has showed anomalous behaviors at Burn's temperature Td, freezing temperature Tf, those are related to a development of polar nanoregions (PNRs). PNR must play a key role in relaxor nature, and obtained results provide insight into the relaxational processes in the PNR and into how they develop below Tf.