The things was black and about the size of a large tennis ball (it was not a bird)and zipped about 15 feet over my house in a dead straight line heading south very fast indeed making what i would call a quite fast mechanical repetitive zum,zum,zum,zum sound that got quieter as it speed away!

I was going at a very fast speed in a perfectly straight line until it disappeared out of sight hence the short viewing time.

I have never witnessed anything like this before. I heard the sound and looked up and it sped over me as I stood in my back garden. I can not explain it, it was definitely not a bird and definitely was emitting the sound. It has made me question many things as I never believed this sort of thing existed I know what I saw!