Stayed up late last night with my husband, was watching TV heard a strange humming sound; our windows were open and we have a glass conservatory. Our Sofa lies just under where the ceiling begins. The reason I clarify this is when we first noted it I was sat on the sofa, we heard the sound and I looked outside and then upwards. As soon as I saw this object, I kept saying, what the hell is that? because it looked like a small stealth plane, triangular in shape silver body with lights on each corner. My husband says he say red and green lights but I was more focused on the shape and body of the object. As I looked up; I was also getting up to go get a better look and as I reacted, the object flew higher up, making a stronger more intense humming noise and when I backed away it came back down almost as quickly as my reactions. I felt observed and when I tried to peek out again it flew away and was gone. I have to say I felt scared, because I felt observed.