I have an LGA775 based system in a mini-ITX attached to the back of a monitor. I am currently running a stock Intel CPU fan, and its getting the job done. When the system is laying flat on my desk for testing, its whisper quiet. As soon as I mount it to the monitor (and the CPU fan becomes vertically oriented) the fan whirls up and down and up and down in RPMs. Its not heat -- the CPU temperature is the same in horizontal and vertical orientation. I believe the fan itself is not stabilized in vertical orientation and is thus making noise.
I've looked at what few coolers are available for a slim miniITX build (factory Intel heatsink height etc) but I can't spend $20-30 per while I try to find one whose fan runs smoothly regardless of orientation.
There are a few from Silverstone and Thermaltake that look like they will fit. But I'm worried about the fan.
The case is too small for me to rig a regular case fan above the heatsink. At least, unless I can find a HS/fan combo that doesn't integrate the fan into the mount (all of the alternatives are modeled after the stock Intel version with the fan integrated into the mount above the heatsink).