In the presence of a steady magnetic field B₀ and a pulsed field B₁ sin omega t, echo effects were observed in powder samples of the metals Cu, Al, Zn, Cd, V, Ag and in the alloys CuCo (0.23% and 0.05%). No such effects were observed in Pb, Pt and Nb powder samples. Various experiments on the echoes are described and some mechanisms for their appearance discussed. The mechanism which most easily describes the experimental data is one involving collective oscillations of the whole sample, that is, many granule oscillations.