When running a game and the side panel to my case is on the fan instantly beefs up in speed and workload to cool the computer. When the side panel is off, it runs normally.
Is this a case of the fan breaking down if I have had it for longer than 5 years? I've also had my hard drive and power supply for just as long.
Better description of your setup would help. How many intake/outtake fans do you have, if any? They might not be providing proper airflow. Clean all your fans and get rid of all the dust in your case like Andrew said.