2007 Audi A4 Rear seat belts wet after rain

I have noticed that after a rain, the rear seat belts are extremely damp or wet. They are recessed into the body of the vehicle. I believe water is somehow getting into the column. I do not notice any water or signs of leaks anywhere in the vehicle or the trunk. I have read that this might be a problem stemming from the sun roof, but I am unsure how to check. I am not sure if removing the headliner is an option either. Please help.