Should my advisor know if I am auditing unrelated courses? Question : Should my advisor know if I am auditing unrelated courses?

Motivation : I am a PhD student in Computer Science and at times, I wish to audit courses which are not at all related to my thesis or research.

For instance:


For Fun : Italian Food and Art
For probable post-PhD jobs (but not related to thesis) - Econometrics, Quantitative Finance.


In general, my advisor is cool and won't mind the hour(s) I spend in the classroom. He allows me to work from home or wherever and doesn't care about "seeing" me in my office so long as I keep doing my work on time (which I do). 

If I tell him about the courses, he unnecessarily might get freaked or worried and might question my intentions (which I can obviously clarify), If I don't it seems as if I am keeping something important from him.
In this case, you should let your advisor know, because the time spent in the classroom is time not spent in the lab. Since he's paying you for your time, if you will be doing daytime activities that will take time away from research he has a right to know about it. On a different note, depending on how auditing works in your university, there may be costs associated with your auditing the course, and he (or his grant) would be covering these costs.

Generally speaking, the more communication between you and your advisor, the better.