We have just finished installing a new 45T and are going through the engine tests, not sea trials yet. The engine runs beautifully, alignment is good, shaft clearance is good, but we are experiencing a hard rattling sound from the gearbox when in gear and at low rpm. The sound largely disappears once we get past 1400 rpm. Is this usual for the gearbox type? I'm hesitant to do sea trials until a better understanding of what is 'normal'. Many thanks.