Three black triangles, glide slowly over my house with strange sound and visual effect.

I witnessed three black triangles of huge size flying slowly over my parents' house.  I was watching out of a window and by the time I manged to pull myself away and dash outside the craft had gone.  This event has stayed with me and been an important influence on my artwork ever since.  I was 8 years old at the time.  This is just one of many strange events that I have witnessed throughout my life.  The triangles were in triangular formation and there appeared to be some connection between them.  A curious sound accompanied the siting; very hard to describe, kind of metallic machine like noise.
Witness indicates that the date of the incident is approximate.  We have assigned an artifical date in June 1960.  PD