There has been past discussion about these issues.
Yes, the fan runs even when powered down. So much for "sleeping", although it supposedly uses very little power in this mode. I still keep it on all the time so it will do automatic head checks and keep things from clogging up.
The banging sound is the ink tubes hitting the metal guide. Some people have wrapped tape, etc. around the tubes to muffle the sound or put the tape on the metal guide where it hits.
My own theory is that the sound is not that of a fan, but rather the hard drive. It is logical that the hard drive would operate constantly.
In my own case, I determined that the clanging sound was caused by the white ribbon cable striking the metal on the *top* -- *above* the white ribbon. (This appears to be a ribbon for power to the head, and is not the thicker ribbon that carries ink.) I applied a soft material, specifically pieces of the lens wrapping material sold by op-tech usa. I taped those to the top of the metal using double sided tape. That is, I taped very narrow strips to the specific part of the metal that is struck by the white ribbon cable. It didn't get rid of all of the noise, but eliminated about 90% of it.