As the power of computers increase, temperature can be a big problem. Most Pentium processors and AMD units have extra cooling systems for the processor as well as the inside of the case.
While most of the time, your fan seems to run at a low speed, there is circuitry to speed up the fan when sensors incate the temperature gets too hot. In fact, I found out my Dell has three speeds. In your Dell software, you should find a set of diagnostic programs (at least one). If you CAREFULLY run these, you can tell how the hardware is working (please don't run any test that WRITES to your hard disk or you can lose everything). Included is a FAN test that will run your fan at the different speeds.
Heavy graphic programs can cause your processor or video section to heat up. Eventually, you can match your activities to the sound of the fan and you will know what activities of yours will speed up the fan.
The only way around this would be to tinker with the "insides" of your computer to replace parts of the cooling system if you can find fans that would do the job but run quieter. I would find professional help in this area since the "penalty" for using the wrong fans can be destruction of parts of your computer system due to excessive heat. One option, if you really want a quiet machine, would be to install a water-cooled system. Once again, if you are not handy working with electronics and tools inside your computer, you can probably get the service department at the store to install it for a price.
By the way, some computers will have a readout that tells you the temperature inside the computer.