Alternative to replacement of anything...
Does the fan turn on based on temperature, or constantly? I am assuming temp. You could try simply installing another, quiter fan on top of the current cooling system. If (as I am assuming), the card is kept cool by the second fan, the loud fan would run less often, and for a shorter period (unless you're gaming, or something else that puts constant demand on the card...). I believe that you could simply draw power from another slot, be it PCI, or what have you. I am not firmilliar with the number of vent holes or position in the back of your model, but you could even install two, one above, and one below / a ~3" one that creates a general cross wind, or diverts hot air from prosc, drives, etc, AND one directly on the sink for the card. If custom cred is what you're after, this is definately custom. Also, it would be about a $20 investmentmaxwhich would not be a big deal if it insufficiently cooled, or did not produce the reduced noise level you're looking for. Depending on what you concoct, you could even disconnect the card's noisy fan in favor of the new one(s). I would leave the built in one connected as a safety net if you didn't have it controlled by the card's temperature. One app I STRONGLY reccomend for this sort of thing is
Temperature monitor which lets you know how your set up is doing temp wise, and can give you an auditory and/or bublled warning if any sensor exceeds the temp you specify. Seems like you have plenty of options for acomplishing your goal w/o shelling much out.
best luck with your endeavors,
b