I heard this bird today that I didn't recognise. There's probably a birding lemmy but I thought I'd try here first.
The audio quality sucks but its a continuous warble that decreases in pitch over about 2 seconds.
I love Merlin! I do go back and delete my old recordings though, they took a lot of space on my phone. Especially because I'm sitting there waiting for the bird to do it again...
It's pretty good at ignoring other noises like traffic and dogs.
I checked it with whoBIRD (FOSS app that identifies bird calls), I disabled location and date and played the sound from my PC. Pretty confident it's a Eurasian blue tit.