You cannot turn the fan off. Fan speeds will increase from the minimum of 2000 rpm due to CPU/GPU usage or possible hardware problems. Install a temperature monitoring applications such as this one:
Open Activity Monitor and set it to show ALL PROCESSES and %CPU to display values from high to low. When you fans get noisy, post screen shots of both.
To address possible hardware issues, run the Apple hardware Test:
You may need to start it with the Option and D keys. It could be that your MBP has a faulty sensor.