Hanging out the clothes this afternoon, I could hear this...gnawing.
Coincidentally, I'd just been playing the opening of the old computer game, The Bard's Tale, which begins with the classic "kill the rats in the inn cellar" quest. [Not to mention some of the most gratuitous breast shots I've seen since, well, the first time I played The Bard's Tale.]
Eventually, after much confused peering about, I found the source of the noise in the tall evergreen just over the fence.
The birds are Corellas (I think), and they're busy eating the conifer seeds.
A step up from rats! [Though, hopefully, no giant, fire-breathing corellas show up, since that's where The Bard's Tale quest ended up.]