Flame deformations in the near wake of an anchoring rod have been studied experimentally using laser tomography and laser anemometry. It is shown that the small scale structures occuring on V-shaped premixed flames are triggered by residual acoustic resonances of the burner when the flame is partly lifted off. This results from a shear layer instability of the wake, enhanced by a shielding effect of the rod on the acoustic held at the exit of the burner. The characterisitic wavelength A/D varies as Re-1/2.