If the fan is noisy, it must mean the CPU is working hard. If it wasn't doing that before, then it must be due to new software being installed. Did you install any new programs just before the fan got noisy?
Run msconfig, then look at the Startup tab. It lists all the programs that start upon you logging in. To diagnose the problem, you can uncheck all of the programs and just leaving your Antivirus program checked. Reboot. See if things improve.
If the fan noise lowers, then it means that one or more of the programs that you unchecked is the cause. Checkmark those one at a time and reboot. And you will soon isolate the offending program.
Run msconfig, then look at the Startup tab. It lists all the programs that start upon you logging in. To diagnose the problem, you can uncheck all of the programs and just leaving your Antivirus program checked. Reboot. See if things improve.
If the fan noise lowers, then it means that one or more of the programs that you unchecked is the cause. Checkmark those one at a time and reboot. And you will soon isolate the offending program.