Only by listening, like a squeaky wheel

Or a young Chiffchaff passing through, peoples idea of a squeak vary greatly

I agree with Robbo. Most probably a Dunnock contact call. You can listen to it HERE

"Internet thinks it's a black and white warbler" - that's the internet for you.

Always look for the most common answer and then work forward from that once you've ruled out that possibility.

In this case - Dunnock.

I'd have said dunnock as for the internet, I take most things from the web with a big pinch of salt.

However, if you know what birds you have around you and a good idea what may be around, but not seen, try British-birdsongs UK web pages, they have a good selection (but not exhaustive) of British bird calls and song.

https://www.british-birdsongs.uk/

Coal Tit contact call sounds like a squeaky supermarket trolley wheel to my ears, may be worth considering

Now Great Tit sounds more like a squeaky wheel to me but both of those Tits have a 2-note sound whereas I think the OP is hearing just the one note repeated (?)

Agree rspbailey but it is like music everyones take on a sound is different. We have found this often when taking groups out birding you could end up with half a dozen descriptions of the same noise,just like the forum lol

Ha ha - well this forum does make a lot of strange noises sometimes

I like to stay current, while raisin the standard, just need the sultanas flag now