Not different from a HDD, in principle, unless there is some hardware issue. But let's assume there isn't and it just files being written to it by a program running in your PC.

The use a program like Treesize Free from http://www.jam-software.com/freeware/ to find out in which folder(s) they are. Just compare yesterday with today and you should see a difference. Knowing what files it are in what folders is a first step to finding the cause.

Kees