There's a bird I hear often (particularly in the morning), outside my flat (urban area), in the woods (broad leafed trees), out in the country, but I've never spotted the bird itself.
It makes a rapid two-tone call, like a squeaky toy being squeezed: "dee-do-dee-do-dee-do-dee-do".
It's quite loud and clear, not a timid tweety sound.
I have looked up and listened to so far are:
Chiffchaff
Great Tit
Firecrest
Goldcrest
It's none of them.
Any ideas?