Hello Rafa,
It sounds as if your garage has diagnosed the start of a failing dual mass flywheel (DMF). If so, it is likely to get worse, so if it were mine, I would treat this with respect, and get a second opinion.
Sorry to be pessimistic, but if this is correct, it is quite a expensive repair, since the gearbox has to be removed, and it would be wise to invest in a new clutch assembly while it is out.
What mileage has it covered by the way?
Kind regards,
Gareth.