What is your laptop sitting on? While you can’t stop your fan once it comes on, maybe you can prevent your computer from getting to the point where it needs your fan. I’ve seen several different cooling docks and other platforms that are raised up and meant to keep the bottom of your laptop from getting hot. I’ve never used on, but they might help. If it’s only when the fan comes on, it seems like at that point, there really isn’t anything you can do. I could be wrong though, maybe someone else that knows a bit more about computers will have some other ideas.