I didn't explain myself well, I didn't mean the sound of the engines, that's quite ok, I mean the high and constant sound. I don't know where it comes from but it doesn't look like engines, it's more like instrument noise. Here is what is too strong(high) using earphones. Now being the high freq reflected by the helmet one should not feel so strong.
I'm starting to think that my ears are too sensitive to high-pitched sounds, but I wonder how pilots endure that sound.