Pb(Zn1/3Nb2/3)O3−xPbTiO3 (x=4.5%–12%) relaxor ferroelectric crystals have been studied by means of acoustic emission (AE) in the 400–540 K temperature range. An anomalous AE activity independent of the ground state relaxor/morphotropic/ferroelectric crossover has been revealed at around 500 K, and it is associated with the “waterfall” feature related to the existence of polar nanoregions (PNRs). The 500 K AE anomaly is attributed to local martensitelike cubic-to-tetragonal ferroelectric transitions within the PNRs imbedded in a nonpolar (cubic) matrix.