My first guess was 'the wind' but that's probably a bit unfair.
Pigeons are fairly distinctive and so whilst I'd describe it as Wuuh-oooh-oooh ooh-ohh it's probably not your mystery bird. Unless the Guuip was it being eaten by a cat.
My bird sound knowledge is very limited to the standard British city birds - crows/magpies/other ones from that family; pigeons; green parrots; blackbirds - I can never remember what noise the smaller ones like robins make. Oh and seagulls.
Guuip sounds like it should be familiar