Before judging people, try to know who they are and what they learnt at school. And for your information I'm reading a book about resonance, sound frequency, etc. I know what reosnance is, but truly .... what's the percentage of chance for it to happen ? And even if it happens, just adjust a little the fan speed to change the frequency of the vibrations. But again, this is a design contest, vibration, resonance, is the job of engineers and the inner structure should be build according to the rest of the case, but this is out of the scope of this contest. Resonance is always a question of right frequency. If you're afraid of it, then I hope you'll awoid all bridges, building, etc, because everything can resonate.