There are several species, each identifiable by the diameter of the little holes they leave. But if you really can hear them munching at your wood then its almost certain to be one of the many kinds of the longhorn beetle (coléoptère in French). If it's localized in a small part of the wood then you can try to kill the buggers. You need to inject the affected area with a solution containing Pyrethrum such as Spritex. But act quickly, they can destroy the woodwork in a roof within a few years.