I use my Blue Yeti on cardioid mode without headphones and the noise picked up is relatively minimal. My apartment is pretty quiet to begin with, but cardioid limits some of the noise and also seems to prevent feedback. (which is taken care of to some degree by the software, but I never have issues when cardioid is on)
Do you remember what the factory default was? I expect most people who aren't au fait with pickup patterns will either leave it on the factory default or put it in stereo (which looks very similar to omni).
