Thank you for your answers.

First, yes, my screen is calibrated (even if it wasn't, there is no reason for any touch detected while I am not touching the screen).

Massing the screen effectively fix sometimes the issue. But most often, 10 seconds after, the issue comes back.

I also notice that the issue appears more often when the environment is wet. So, I think when I have time, I will try your solution, dzano.