Misterious dissonant humming_original.wav

Here is another mysterious recording. PRobably around 9-10pm.
Recorded from my room, windown was open, hoping to pickup any interesting sounds.

The sound is quite faint but can easily be seen in the spectrogram using a program like Audacity. You can easily see it here also using the Spectrogram display in the sample window.
Barely noticeable when played at normal speed.
I was scanning through the recording to check if I had anything interesting, so I was playing it in Audacity at 3x speed. That is when I noticed the dissonant hum. Would not have noticed it if playing at normal speed.

The sound is present from the start of this file but increases in intensity and then suddenly stops at about 25s.

Does not sound like a car/motorbike/train/airplane. I don't know what it is.