strange mixer noises in the early morning

A few days ago, I woke up in the early morning (before 6 am) because I heard a strange noise. I thought someone might be drilling holes in the house or whatever. But I also thought, this could be coming from my studio.

So I got up and I discovered that the sound is coming from my speakers. And the meter on my mixer was going into red. The sound was a bit like an LFO motor-like synth sound, but all my synths were off. I tried to turn a few knobs on my mixer and I discovered that it was the 1st channel that generated that noise. I could turn down the volume, and I could also change the sound a bit by turning the Gain knob. But then I switched off the mixer and went back to bed.

I thought it might be because the mixer was on for a long period of time, maybe a temperature problem. I don't even remember when I turned it on the last time. But now recently I turned it on again in the evening, and in the next morning, again at about 6 am, I had the same rude awakening

Does anybody know what the problem might be?

I made a video, sadly the noise is not very loud on that, but in reality, it was quite loud.
https://www.youtube.com/watch?v=WbX6jBihr5s