When I received my Mini I turned it on to determine if it worked but quickly turned it back off and began the operation to remove the old hard drive. It honestly did not run long enough with the stock hard drive for me to notice if it was noisy or not. The solid state drive I installed is dead quiet and is suppose to pull much less power than the stock drive it replaced. Mine is what I would call a "lean, mean, music server, machine."
I purchased the Mac Mini because I decided on the Tranquility USB DAC and Eric Hider of db Audio Labs recommended the Mini as the best choice for a music server. Eric told me if you are basically planning to use a Mini as a dedicated music server you do not need the most powerful, latest edition of the Mini. He recommended a Mini with Snow Leopard Operating System and to replace the stock drive with a SS drive.
If your intentions are to use the Mini as a dedicated music server and maybe browse the net I would recommend you purchase a used machine on Ebay. Replace the hard drive with a SS drive and while replacing the hard drive bring the machine up to 4 gb of ram if it does not come equipped that way. There really is no need to spend maybe $1000.00 on a fully equipped brand-new Mini unless you want to and note it will still have a stock drive! 4gb of Ram is available on-line for less than $100.00 and a SS Hard Drive is around $125 or so depending on size.
Go luck on your decision and no matter which way you go I am certain you will be happy with the Mini.
Ken