Originally posted by: Imp
Aluminum isn't suppose to be synonymous with silence on account of its wait. Still, doubt it really matters in the end. If you want silence, you'll have to get creative with foam, cardboard and rubber bands

. I have a crap budget case, but managed to cut the noise down from jet engine to unnoticable by doing patching up some redundant holes. I'd just look for a good case and do my own mods.
There may have been a time when aluminum cases were prone to vibration/rattling, but you rarely hear that complaint anymore when dealing with today's high quality aluminum cases. I have two Cooler Master aluminum cases, and both are silent. No rattles whatsoever (ever), and the only noise I hear is the CPU fans. And I can
barely hear those.
I suppose there are some really cheapy, flimsy aluminum cases out there, but why buy a poor quality case anyway?
Re the mention of rubber bands -- presumably for HD suspension? -- some people think they can lead to read/write problems with some hard drives because they allow the drive to 'bounce' around a bit. I've never tried them myself, but some people feel it can be an issue.
Like Imp said, start with a high quality case, and do a mod or two if really necessary, and you should be fine with aluminum as a case material. For aluminum, high airflow and silence, you'll prolly have to consider one of the pricey Silverstone cases.