Built this year from mostly excess parts: P4 531 (3.0GHz), MSI G31TM, GT520, ATX 300W PSU, Intel CPU headsink/fan + 1 80mm CoolerMaster SuperFan, DVD drive. Went together pretty easy except for clearance between PSU and DVD (noted in manual and elsewhere). Disc player cases have lots of depth variation, so seqarch for a short one. A right-angle SATA connector would have helped, too.
As expected, CPU fan was pretty noisy at first. Got back to basics on improving airflow and baffling before getting more expensive hardware. In the picture, you see a block of foam that has been carved to provide both a duct to the grill opening on the top and noise baffling. Grill holes on right side of case are sealed with clear packaging tape except for the 80mm fan in the front position. Airflow is top/front/side to back with positive case pressure. Not showing is a block of foam that goes accross the top of the case in the back to prevent warm air from recycling back to the top inlet.
System runs pretty quiet now - can't hear from more than about 4 ft away. SpeedFan reports the CPU a couple of degrees cooler than before the foam was added, and 20% reduction in CPU fan speed at idle (approx 3400rpm down to 2800rpm).
P.S. Limiting the fan speed can be dangerous to your hardware - better to improve airflow and baffling first! Fan settings need to be factored with CPU utilization. In my case, CPU is idling at 2-3% utilization most of the time. Playing a DVD brings it up to an average of about 10% with short bursts much higher. XBMC when playing music reports 13% utilization as another benchmark.
Want an easy way to see how good your cooling is? Run the Windows Experience Update while monitoring with SpeedFan. CPU utilization on my system was 80% to 100% on both cores for well over a minute. CPU temp increased from 50C to 74C, and fan speed from 2800rpm to 4000rhttp://img267.imageshack.us/img267/3047/p1000452001.jpghttp://img840.imageshack.us/img840/2170/p1000450f.jpg