Do you fee that your laptop is overheating as well along with the fan noise?
And do you hear the fan noise all the time or it happens when you play games or do some CPU intensive work like watching HD movies or something?
Might be dust clogged in the cooling fans, hnce greater rotation effort is resulting into excesive noise. Clean it with blower, dust is the primary reason behind the excessive sound of noise or excessive CPU load.
Avinash, try blowing air from a blower into the exhaust ports of the lappy. Hehe, these are the ones from where warm air is ejected!
Reverse direction blow, with a Eureka Forbes vacuum cleaner in blower mode.
Might just solve the problem. Else you'll have to clean manually or replace the fan!
Please don’t try to repair it your self and experiment with it, find a Sony service center and get the service done, only Sony engineer guy or gul (my wife is engineer working in Sony service centre for lappy especially for VAIO) can open it, because its an expensive lappy.