We have performed a set of experiments on the localization of unstable seismic boundaries observed due to acoustic measurements of a loose medium under dynamic loading. The correctness of used procedures and acoustic equipment is experimentally tested. Thus, we have found that 1) at the same vibration source pulse and continuous quasi-harmonic sounding provides identical results (which allows a correct comparison of seismograms obtained by these two types of sounding signals); 2) assuming that the surface source platform maintains a continuous contact with ground, generated impulses of load-compression and unload-rarefaction types provide absolutely identical seismograms of opposite polarity. This bears evidence of the sounding linearity, i.e., in such experiments an acoustic sounding process induces no nonlinear effects by itself. Crosshole acoustic measurements are used to reveal a considerable velocity heterogeneity in the studied block, where velocities of longitudinal waves vary from 330 to 470 m/s. Crosshole acoustic measurements of the wave filed discover a sufficient negative influence of both standing and traveling tube waves. They are found to appear simultaneously in the same borehole and have different spectral composition and damping constants. The boundary induced by dynamic loading of the medium corresponds to none of seismic boundaries observed at acoustic measurements of an undisturbed medium and however it falls within the region of the tube wave coda. Thus, the nature of induced boundaries is still obscure.