Take a look at
www.endpcnoise.com and
www.quietpcusa.com for quiet cases and other parts. I record with my PC in the same room and these guys helped me get great results. Here are a few tips:
- Get a case like the Antec Sonata designed for low noise
- Add acoustic treatment inside the case to dampen noise
- Larger fans make less noise because they run lower RPM for the same air flow.
- Big CPU and Video Card coolers with more surface area are quieter
- Quiet and silent power supplies are available
Try to determine the sources of noise in your current setup. You could unplug fans, etc. to narrow it down. Don't forget hard disks - check them both idling and accessing data.
Jeff