ID from a bird call

Morning all, apologies if this is not the right place but not sure where to ask.

On my morning dog walk in the Carmarthenshire countryside, I came across this lone blackbird-sized bird sat atop a tree making a call I didn’t recognise (see video, sounds a bit like a thumbnail across a comb). When it flew away, it seems to fly with a slight undulation (not as severe as a Great Spotted Woodpecker).

Any ideas?