Windows 11 laptop fan runs fast and loud for no reason

Windows is sometimes set to a "Best Performance" power mode, which locks your CPU at high speeds and generates unnecessary heat, even when you're just browsing the web . Switching to a "Balanced" plan often solves the problem immediately.

It's definitely jarring when your laptop's fans suddenly sound like they're preparing for takeoff, even though you're just browsing. The good news is that this is a common issue on Windows 11, and it doesn't necessarily mean something is broken.

While CPU is low, check is there are high usage on memory, disk or network? 

If this happens only while you're browsing, try clearing out browser data, check if any browser tab is using crucial amount of memory. Nowadays browsers show these data for specific tabs, while hover on a tab.