Yeah I'm probably going to see if I can't find somewhere else to put them next year. Thanks for all the good suggestions.
And just to clarify, it's not about not having the space to put them, but they have to be somewhere where the noise isn't an issue and they don't stand out. Also the good thing about the attic is that it's probably the only room where it's okay to have a "messy" setup with an old 12" LCD display hooked up to it at all times.
At this point I'm considering building an isolated box for them, with proper cooling, and placing that outside behind the house where it's not visible (have a pretty nifty storage space underneath the porch).
One thing to remember: Your backup drives should be in a place that is safe from burglars, so the attic is a good place for them. Which means you can do backups cheaply with a cheap big USB drive connected to the Mini in the attic. (If your house burns down you probably have worse things to worry about).