If you have the Dell XPS 13 Ultrabook with the optional CORE i7 processor, and noticed some unusually high fan speed and only doing the simplest of tasks (sometimes just being in idle Windows), then you weren't along. Turns out many more people were having this issue, and Dell has pushed out a BIOS update fixing the problem.
At the source link below, you find the A03 BIOS update, which delivers "an updated thermal table which dictates fan speeds and trigger temperatures." Evidently, these machines have a tendency to kick the fans into high gear prematurely. So grab the 4 meg update below at the source link.