We present experimental data of the motion of a cylindrical slider interacting only by friction with a polished horizontal tray. The tray is harmonically shacked in the horizontal direction. Below a certain threshold of the driver acceleration, the slider permanently sticks to its substrate due to the static friction. Above that threshold, the observed slider dynamics is periodic (synchronous with the driver oscillation frequency) but not wholly harmonic: for driver accelerations little beyond the threshold, the slider velocity signal is quasi-triangular. A Markovian model shows that, with increasing driver acceleration, the slider motion increasingly tends to be harmonic again, though with a prominent phase difference respect to the driver.