Hello timtam84,
Thanks for using Apple Support Communities! It looks like you're noticing the fans on your new MacBook Air are running fast and loud and you're not sure why. We'll be happy to help out.
Activity Monitor can help with determining why this is happening, as it sounds like an app is using more of the processor than needed. Here's how to check: See how apps affect Mac performance, battery runtime, temperature, and fan activity
Since you mentioned the only app you've added is a virus and security protection app, that may be what's causing the issue.
Installing protection such as that is entirely up to you, however, you'll find that the macOS has security included. Read more about that here: Security. Built right in.
We'd suggest uninstalling the Norton application according to the app developer's instructions.
Then reset the SMC, fo.lowing these steps: How to reset the SMC of your Mac
Use your Mac for awhile and see if you are still having the same issue. If you are still having the same issue with the fans running fast and loud without that app, then you'll want to contact Apple Support for some assistance. Get Support
Here's some other great information about keeping your Mac secure.
Protect your Mac from malware
Find, buy, and download apps in the App Store on Mac
Ways to keep your information safe on Mac
Take care!