Bird call with three notes

Hi there,

Just heard a bird calling in my garden that I've not heard before. The song appears to be three notes in quick succession, then a long pause before repeating it. The tone of the notes sounded almost electronic, like a beep, and if I listened closely the final beep of each 3 note phrase sounded a little lower than the first two in pitch. I managed to get a very short clip of it as the app I used got rid of the rest. In this clip the bird paused a bit before the final note - usually it just beeped three times without pausing.

Here's the call:

Any ideas what it was? I live in Somerset but as said before, I've never heard this call before.