seat belt damp

We had a ton of rain here a few nights ago and I mean it rained hard. I didn't drive my car until a couple of days later and noticed as I put on
my seat belt that it was cool and damp. Nothing else was wet (seats, floor) and I opened the sunroof and everything was dry up there too. It's an 01 330Ci and I have noticed tiny amounts of water getting in the window when I go through the car wash/dryer. Any idea how the seatbelt could have gotten wet? Thing is I had a mould problem in my last car and that's the last thing I want to deal with again. Thanks, Jonathan
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.