Good afternoon Rodrigo3tres,
Welcome to the Apple Support Communities!
It sounds like you are hearing noises in the videos captured with the native Camera app on your iPhone 12 , and we'd like to help.
Can we ask a few questions about your specific experience?
When did first notice issues with the videos recorded on your iPhone?
How many videos are affected?
Is your iPhone updated to iOS 15.1.1?
If you have iCloud Photos enabled, when you play these same videos on your Mac or iPad, can you still hear the noises?
Try quitting the Photos app, and restarting your iPhone.
Then test by playing a video that has the noise issue. Try several videos to confirm the issue isn't a corrupt file.
The resources below will provide some guidance:
Close an app on your iPhone or iPod touch
Restart your iPhone
Update your iPhone, iPad, or iPod touch
If the issue persists, please reply to this thread and we'll do our best to help you!
Take care.