You have to go to Velia, Rent a Flute from Pulvio, go to the Guild NPC Laiano Pietro,he gives you a daily called something like "house & mouse" or something along these lines, finish the daily, turn it in, knowledge aquired, return the flute, happy life.

The Flute game point is to AVOID the notes using left and right click.

if you are lv56 you probably don't have the daily quests in velia heidel and idk if other cities, I took a lv14 alt, rented the flute and the daily is there.

Level 57 and I also found the flute quest from the Guild Manager, Laiano Pietro near the marketplace in Velia.

can't get the quest right after taking flute, idk why. lvl 61

edit: just like the guys said in the comments.. make sure ALL quests are visible in "O"

Primero que nada, háganlo con la Shai. Alquilen la flauta de Pulvio y luego vayan con Laiano Pietro y agarran la misión de los ratones. Se equipan la flauta y esquivan las notas musicales.

For anyone having issues with the quest not showing up after making sure all quests are visible, if you have the flute equipped it will also not show up. So you need to have it in your inventory.