Lake Ice Periodic Expansion Wavefronts

I was at my brother in law's place on the shore of the large lake beside Westport, Ontario, Canada.  An absolutely amazing phenomena happened.  We stood on the lake for about 15 minutes when an expansion wave went through the lake and passed under our feet at a speed that felt like the speed of sound.  Everyone has heard cracks when on the ice - but this was something completely different and very rare.  It seems that the ice at this early stage in its development has not developed any major defects or cracks and when it undergoes expansion due to further freezing as the night falls.  The wave of molecular expansion can be heard a mile away approaching and felt as it moves your feet a fraction of a milimeter and then hits the shore.  The sound is sort of like a light sabre sound just under your feet.