If you are in the UK then there could be two possibilities, both of them owls unless it's an early Vixen having a scream.
The Barn Owl can more than likely be discounted (do you agree NF?) as it's not called the 'Screech Owl' for nothing - and it's a bird of the open country.
The Tawny Owl is the most likely contender as it's fairly common in towns now and the male has a wonderful atmospheric hooting song, much used in horror movies. He starts off with a 'hoo', followed by a pause, then a 'hu, hoo-oo' all shaky and quivery at the end.
The Little Owl makes a sound that is nearest to the two notes you descibe. The male gives a high-pitched questioning hoot with an upward inflection. It is a country dweller, but is also in towns.