Youtube is testing a new piece of tech that will equalise the audio level on mobile devices and hopefully in the future, this will be extended to other platforms like smart tvs.
For those older enough to remember, when the BBC used to be in charge of various kinds of standards, including audio quality on channels, the sound levels were always level, because they ensured that. Then sat/cable tv came along and the standards were binned and to this day, audio levels across channels are different and even on the same channel, the levels are different, ie when ads come on and this is no different to youtube.
Bring on audio levelling, I say! And no more adverts blasting out.