I love how this thread is increasingly turning into a gender thing, when in fact this issue could come up with any roommate. Or even in reverse...
My computer's noise was driving my husband up the wall recently. So after a fair amount of pestering from him I finally armed myself with some canned air and carried the system out to the patio, opened up the case, and found... that it was fairly clean inside. All I really needed to do was clean the air intakes on the *exterior* of the case. It was that simple and took seconds. The noise level dropped considerably. It went from being all we could hear in the living room to running near-silent.
So clean the outside. If that doesn't work, open 'er up and dust. And then yeah, if that doesn't work, I think this comment above is great. Consider a case with better airflow and/or different fans. I also can't say enough good things about having your OS on a SSD -- far quieter and much quicker. I did that on my latest build and it's fantastic; well worth the trouble of reconfiguring your files.