I toured professionally as a drummer with a tech metal band and played with a click track every night. I used Ultimate Ears (high-quality earbuds) with ProTools through a rack amp. I had guitar tracks going behind the click track (metronome) for reference and let's put it this way... the reference guitar tracks had to be louder than the actual live amplifiers/PA and the click track had to be even louder than that. On a scale of 1 to 10, relative to the loudness of the vast majority of electronic music players (computers/mp3 players/phones/etc.)... I'd say my click track was at least 17. It hurts my ears just thinking about it now... constant TICK TICK TICK TICK TICK for 30 (sometimes 45) minutes every night for weeks at a time! I don't wish that upon my worst enemy.
If it was another style of music there's no doubt I could have had it turned down to a fraction of what it was... but it was tech metal so it was always loud and heavy and all over the place. Most of the time I'm playing upwards of 300 bpm and the tempo and time signatures were always changing so the click track was necessary. I remember I tried turning it down a few times and it didn't work out so well haha... Bye bye hearing! I miss you.