I’ve a Sony Vaio SB series, the one with double graphic cards. I just noticed that on Windows everything was smooth but on Linux the fan was running at maximum speed all the time and the laptop was very hot.
After some investigations I understood that this behavior was due to the second graphic card which was on meanwhile the integrated graphic card was working. After a bit of googling i found a nice explanation of my problem reading this page on the ubuntu help.
If you have the same problem just put this line:
echo OFF > /sys/kernel/debug/vgaswitcheroo/switch
just before the exit 0 command. This will shutdown the second graphic card as soon as the computer boots, increasing battery life and decreasing fun speed, and thus, noise.