Buried into the airport utility is the diagnostics on your TC..
Let me try to show you everything in one go.. click on your TC and click edit on the summary.
You will then be able to open the diagnostics.
You can open this and find the temperature setting as well as fan info.
Fan speed should be like mine.. about 1700 RPM.. and like Bob I cannot even hear it over the top of background noise.
It also might show you a bad thermostat or bad fan.. There is a lot of info stashed away in there.
Knowing of course what is wrong is not fixing.. but it gives you help to get it replaced if you are outside of the 14day return with no questions period.
Return it to apple for replacement.