I'm wondering if anybody knows how the 3-wire cooling fans that are pretty much standard work. I see that some are rated at different RPMs and CFMs. Who controls how fast the fan goes, the MB or the fan itself? If I replace the fan in a PC with one that is faster or quieter, or whatever my goal is, will the fan speed increase based on the system temperature only, or does the MB sense the temperature, and set the fan to a certain voltage regardless of the fans rating? My specific problem is that I want a quieter fan in my Shuttle PC. The PC is one of those little systems Shuttle makes, the SK41G, which only has a small fan for the power supply, and one 80mm fan for the rest of the system. One of those fans is real noisy, and I'm hoping it's the 80mm since I can easily replace that one. But I need to be certain that the system will continue to cool properly with a different fan because that one fan also cools the heat sink on the CPU. Another problem I have is I believe my modded Tivo is overheating. I'd like to replace that fan, and in that instance the noise issue is not a factor. But I need more cooling because the Tivo acts up even when it thinks the temperature is 37C, which is in it's normal operating range. I suspect that the drives are getting to hot, but the rest of the system is ok, or something like that, and so the system doesn't realize it's too hot. Seems strange, but if I remove the cover it drops to 34C and all is fine. Both the Shuttle and the Tivo use the standard 3-wire connections. I'd like to find a good fan for the Shuttle that will cool it as much as needed, but be really quiet, and another fan for the Tivo that will basically run all out all the time and keep it real cold. Any suggestions, comments, or advice is welcome.