Hello Junipter8,
While it is not possible for your iPhone to receive transmissions from other people without making or receiving a call, it could be possible the noises you are hearing are from another app that might be open.
You can use the steps in this guide to close all apps and see if you still hear the sounds: Close an app on your iPhone or iPod touch - Apple Support
Phone X and later
1. From the Home Screen, swipe up from the bottom of the screen and pause in the middle of the screen.
2. Swipe right or left to find the app that you want to close.
3. Swipe up on the app's preview to close the app
We also recommend restarting your device and keeping it updated as those steps assure you have cleared out any minor software issues and are running the most current version.
Restart your iPhone - Apple Support
Update your iPhone or iPad - Apple Support
If you still have questions, reach out to Apple Support directly, as this may require closer guidance: Get Support
Cheers!