2 equilateral triangular shapes formed by white lights at each point, spinning slowly directly above us, all sound around us stopped

UFO sighting  1979/80  I was about 6, I was with my mum, my Gran, my aunt, and my brother.
It was dusk, a beautiful still evening,  a cloudless sky and we were all walking along Heacham beach, in Norfolk, near to my gran's house at the time.
We could hear the sound of the sea and seagulls as expected when on the beach. Then suddenly, my brother pointed up at the sky as he’d spotted some strange lights above us in the sky, at which point we all looked up, and then we were all suddenly aware that all sounds around us had stopped and all went completely silent, it was a bit like being in a soundproofed room.  We were able to hear each other talking but all external sounds were gone.
Directly above us, and not moving or making any sound, and about the height that a helicopter could be hovering were 2 equilateral triangle shapes slowly rotating.
At the tip of each triangle was a white light, but I couldn’t see anything in between the lights, such as a solid object, it was just the same colour as the dark sky around them.
We all stood and looked at them and all said the same, that it had gone completely quiet. We all speculated as to what it could be, helicopters seemed to likeliest due to their height and that they were hovering directly above us, but it was impossible due to the complete lack of any sound whatsoever, and also that the lights were spinning so slowly.
We must have stood there for about a minute just completely transfixed by it all, and then suddenly, the sounds returned to normal and the 2 sets of triangle lights sped off through the sky and out of sight over the horizon quicker than I have seen any craft move, ever!  We were all completely baffled and we raced back to my grans house to tell my grandad.  He laughed at us and said it must have been a plane or helicopter of some sort and would not believe that it had to be a UFO, but, we all knew that there was no other explanation, and we had witnessed something very strange.  My mum asked me to sit down and draw a picture of them, which we probably still have somewhere.  The following day, there was a photograph in the paper of exactly what we had seen, and a report of many other having seen the lights, so someone else had taken a photo, and we had proof.  It must be in a newspaper archive from the time.
I have been trying to remember when it was and asked the others who were there and we think it was 1979 or 1980.  It was warm enough to be walking barefoot on the sand, we didn’t have coats and it was late, maybe 9 ish.  It was probably summer as my brother and I were off school.
I often recount this sighting and think it’s about time I officially log the experience, hence this email.