Yes, AFAIK and IME it should be absolutely quiet. As I said before, there are electrical components that can make strange noises when failing, but this is such a simple device that I would not expect that. If the pitch is higher than a disc spin-up and you are hearing a mechanical like sound, that really does suggest the fan. The Q's fan is a Delta, which is very good quality. But any fan can fail, and of course there can be an issue if it was incorrectly mounted (or replaced improperly?). But if it is running while turned off then there is an electrical issue and something seriously amiss. Are you feeling any kind of airflow with the fan turned off? (Turn the machine on fully cooled, be sure the temp is at the lowest setting, remove the bowl and put your ear near the top of the unit for a few moments.) I suggest an email to Arizer support.
I don't know the look of the Extreme prior to the Q, but I think there is a separate thread here for that machine which probably has pics. The Q's LED is blue in a ~1/4" aluminum frame held by a black bezel faceplate with white lettering. The shell I think may be similar but is shorter than previous generations.
Re combustion, why are you so far up at 250C???