Saw and heard two objects fly across Grebe Lake in Yellowstone N.P. at an amazing speed with a strange sound.On August 19th of 2014, I was vacationing with three friends in Yellowstone National park. We decided to hike to Grebe Lake, which was about 3.2 miles from the road. We took off around sun up (6:00 AM) and drove from Fishing Bridge campground to the trail head at Grebe Lake.We hiked into the lake and arrived around 7:40 AM. There was fog on the lake and we waited for it to clear and set up our fly rods and equipment. I took three pictures of the lakes and my friends and we moved into position just to the right of where the trail enters the lake. I was standing ankle deep in the lake and my friend was standing right next to me. Our other friends stood together on the other side of the trail entrance, about 100 feet away.I heard a sound that made me think it was an aircraft in the distance coming directly towards me from the direction of the trail. I turned and looked directly over my head and directly behind me. The sound increased and passed directly over my head and moved towards the lake center. I saw two objects moving over my right shoulder and directly across the lake from me. They moved in a tight formation of one slightly ahead and right of the slower one. They looked identical in shape, size and color. They moved at the same speed. They seemed to be the source of the sound I had heard, as the sound changed direction with their passing and the sound diminished and stopped as they disappeared. The movement was faster than any thing I have ever seen. They did not change aspect as they moved and seemed to be the same shape and color as they went over.The sound was not an engine sound. It was not a jet sound. It reminded me of something large passing through the air, more of a pulsating sound. It was loud, but nothing like a rocket or jet engine sound.The two objects looked round with a somewhat pointed nose. There was no contrail, smoke or vapor trail. The angle in relation to the ground appeared to include an impact with the hills directly behind the lake. There was no impact sound or bang of any type. It was very quiet when they disappeared. There was no ambient noise on this desolate lake. There was no flash or smoke associated with their disapperance.I began yelling to my three friends and asking if they had seen the objects. They said they did not see it but did hear it pass over us. One friend said it sounded like "incoming artillery fire" when he was in the military. As we spoke about it we heard the sound again. This time not as loud and not directly over our heads. It seemed to be off to the right of the trail head as you approached the lake.There were at least two separate groups of campers on the lake. We approached each group as we fished and walked around the lake. The first group we met was a male and female, couple. I asked if they had hear anything this morning right after the fog cleared and they said they only heard me yelling. They asked if I caught a large fish.The second group had approximately four young adults. When I asked if they heard anything odd, they said "No, why"? When I said I saw something strange, the one young man said was there a flash of light and a song? I didn't respond.A few days before we watched an F-22 conducting a close ground practice for an air show or something in Davenport, Iowa. These things were much faster moving and made very little sound when compared to the jet.I have been in many small and medium aircraft and helicopters. I've sky dived from 14,000 feet. I attended and video taped the Paris Air Show in the early 80's and sold the video's through the magazine "Aviation News and Space Technology." I was a police officer for 32 years before retiring in 2006. I have never seen anything like this before.Sent from my iPad