The fan may be on its last legs and dying. Depending on how much you're attached to this laptop, you can buy a replacement new fan, a replacement used fan salvaged from some else's dead laptop, or just get a new laptop.
http://www.ebay.com/itm/Brand-New-Sony-VAIO-SVT131100C-SVT13112FXS-SVT13113EN-Cpu-Fan-Heatsink-/251917230399