Wood pigeon - odd sound needing identification

Sorry if this is the wrong part of the forum, I'm new here!

We have a large number of birds frequent our garden as we live in MK and so are surrounded by a lot of green spaces, so I thought I had heard most noises!

At the moment I am being woken up by a wood pigeon either in or on our roof from 5am until about 9am. We don't want to go in to the roof to investigate if it's a nesting sound which is why I wanted to ask the question. We wouldn't want to disturb and will go close up the roof after breeding season.

The sound it makes goes on for a very very long time and is a low loud hurrr hurrr hurrr hurrr hurrr hurrr. It is the same pitch and maintained rhythm.

It's not the normal call, or the slow cooooooo coo, when the male is bowing to the female to mate.

I initially assumed it was mating but it seems to go on for much longer (5 minutes + at a time at least) and I cant hear any associated wing beating as the male tries to keep his balance!

Any help would be appreciated!