The Volcano 7 uses a variable speed fan hocked to a temp sensor on the heatsink. The hotter your case gets, the faster the fan runs. If you add a few low RPM fans that are pretty quite, it will likely make the Volcano 7 run a little quieter. Now likely that second temp sensor is your Northbridge and it usually runs a few degrees hotter than the actual case temps. Your case temps should be about 2-5'C above room temp.
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