How many kilometres did you with your car from new ? I think, as for all new cars, things have to get in place before working properly.
It's hand made car so be patient with it and you will be rewarded. Mine +4 2.0 2008 begin to ride properly after 3.000 kms.
Regards from Belgium
...and mine (9000 km since new) has "sounds" coming and going. I think, it depends a lot on meteorological conditions, because the wood reacts with humidity and temperature.
Just learn to love it, same as I did
Salut from Lėtzebuerg,
Ivo
PS: quarre, where in Belgium do you live?
)