Fattysb,
Thank you for letting us know what's going on with your iPhone 11. It appears that when you start recording a video in the Camera app, there is no sound for 10 seconds then the sound is normal. If you haven't already, we recommend seeing if a restart will help: Restart your iPhone It can seem like a simple step, but it can sometimes help resolve issues.
Also, you'll want to make sure your iPhone 11 is fully updated: Update your iPhone, iPad, or iPod touch If there is an available update, you'll want to make sure that you back up your iPhone 11 first: How to back up your iPhone, iPad, and iPod touch
Best wishes to you.