There is always a fan spinning which you can hear, not so bad but if you are recording music then your mics may pick up the noise.
Turning it off is an option, but rather then the heads clogging (if you only switch it off for a short time they shouldn't), when you switch it back on it will go through a start up routine which will consume ink each time.
I don't understand WHY a fan needs to spin (or hard drive if that's what it is) continuously whilst the printer is in standby, surely there is no need for it if the printer is asleep .. but it does!