What was causing the rocks to vibrate? Do you mean a physical vibration or an electrical/energetic vibration? At what frequency? A low hum? I would not know if you experienced a commercial product or something of natural origin. Were these actual rocks? Did they feel heavy or light? What size were they? Was there anything to indicate they had an opening inside? Did they have a pebble (smooth) or irregular surface?

Have you ever heard of the Ringing Cedars in Russia and the lady called "Anastasia"? When some of their evergreens out in the forest get over 500 years old some become so full of cosmic energy they start ringing.