Crackle sound

Hi - Firstly, I have never had a car get so many compliments. It is a pleasure to drive. I have experienced some minor leaks but nothing I can't live with. However, there is a very faint rattling or crackle sound coming from the dash area when the car starts to exceed 70 km or so. It is fairly faint but evident. Especially when the roof and windows are up and no music is playing. Has anyone else experienced this noise?