I'm currently in the process of upgrading my computer and studio, and one of my biggest peeves in my current machine is how much noise it makes. I'm currently using an Antec Solo II, which was billed as a silent case, but it has a top vent over the power supply that makes the PS fan noise leak out, and the fan is pretty loud, so I totally felt ripped off. I previously used an Antec Sonata II and THAT was a beautiful, quiet box (except that !@#$ drive door hinge kept breaking all the time). Which silent mid-tower cases should I be looking for these days?

I use Corsair Obsidian 550D cases. I really like them for the most part. The only thing I'd probably change would be to make it wider for more space behind the motherboard and less optical spots in favour of more HDD spaces.
 
I got my wife a Fractal Design Define R4 which is basically the case I want design wise but it uses more plastic on it than my 550D's and I find the components aren't as good. Lots of little details such as I love that my 550D has toolless hard drive holders.
 
The other thing you should look into is fans that are actually silent. Everything in my cases is now Noctua. They are expensive but well worth the money. Absolutely silent case/cpu fans.

I have only had issues with noise from case fans (bearing degradation). The PS making noise is a bit concerning, and not sure what wattage/model you have. The case itself is fairly moot to the objects inside it (mounted properly), what it sits on, and how easily air can flow through it. I would be more apt to scrutinize the PS before looking at cases as a "solution."

The Fractal Designs R4 define case I have on my primary DAW is silent, the only real clue it is on is the blue LED power light.

mettelus
I have only had issues with noise from case fans (bearing degradation). The PS making noise is a bit concerning, and not sure what wattage/model you have. The case itself is fairly moot to the objects inside it (mounted properly), what it sits on, and how easily air can flow through it. I would be more apt to scrutinize the PS before looking at cases as a "solution."

The PS doesn't make any extraneous noise, it's just the fan blowing air, but it's considerably louder than my previous computer's case and PS.

have a look at Gelid for case fans. I have their case which does not have any noise proofing but all my fans are Gelid silent and I get no noise to speak off.

I had a silent case until a moron bumped it with a vacuum cleaner. I do not let them in the room anymore. It's still quiet just the occasional slight buzzing that a little tap to the bottom of the case resolves. I need to open it and I'm sure I could add a little something t make it stop.
 
Watch out for housekeepers!!
 
J

More holes in a case = more noise.