I'd never as much as seen one before. Let alone heard one, they're so loud! And their buzz is very very low, I can't think how to describe it. When I first heard one fly past my window I actually thought someone was using a power tool nearby.
Well Mummy hornet flew into my kitchen a few weeks ago (my god she was huge!). I closed the door to the rest of the house, opened the outside doors and left her to it and she was soon gone (thankfully did not decide to nest in my kitchen).
Then a day or so later I saw her crawling into my bird box. Fast forward a few weeks and there's a few of them appearing, they keep coming into my conservatory of an evening. Fascinating creatures and I can see their nest in the hole of the bird box, just looks like a wasps nest really, cylindrical, paper-mache-like.
I do have a question, will I disturb them if I use my compost heap, which is directly underneath the box? I don't believe I will, I am not tall enough to be in their flight path to and fro, there's roughly 2-3 feet (I think!) between the lid of the compost bin and the bird box.