Mysterious bird call (is this even a bird call?)

I heard a strange noise today - while I wasn't able to see what was making it, I managed to take a recording. Does anyone recognise this noise? Is it even a bird? Here is the recording, the noise starts at 4 seconds in: https://voca.ro/19YoBEa5p I'm completely puzzled, so any help would be appreciated! The recording is a bit quiet, so apologies if it's hard to hear.