Grounded pyramid formation of 3 objects alternating in colour and making a grinding noise holding a slow steady course.

My brother and I were walking along a trail through a forested area when we heard a peculiar sound. The sound would have been similar to the sound made by dragging two heavy concrete objects (one on top of the other) in different directions. It was loud enough for us to take notice from some distance off. As we walked the trail we realized the sound was getting louder so we were getting closer. We came to an area in the forest with a small overgrown field and took note of the fact that the sound was coming closer and was on an intercept course with the field. This would give us the opportunity to check out what was making the strange sound. A sort time later three objects emerged. The objects were on the ground. The were in a triangular formation, they looked like pyramids tipped on their sides, they alternated in colour between brown and orange, the colour seemed in radiate at a low intensity from their interiors, they were about 4-5 feet tall and moved a 2-3 mph. They maintained a constant course and speed. We ran after quietly freaking for a couple of minutes.
Date is approximate.  PD