Various users complained that the incoming call audio quality on both sounds strange. On Apple support site , they tried to explain the method to solve this problem with some steps.
If you hear distorted sound or no sound from your iPhone 7, go for this method!
If the speaker on your iOS device doesn’t work as expected, follow these steps. Try again after each step:
Go to Settings > Sounds and drag the Ringer And Alerts slider to turn the volume up.
If you hear sound from the speaker, follow the rest of these steps. If you can’t hear sound from the speaker, contact Apple Support.
If your device has a Ring/Silent switch, make sure it’s set to ring. (If you can see orange, your device is set to silent.)
Restart your device.
Open an app that has music or sound effects. Adjust the volume with the volume buttons or the slider inControl Center.
Go to Settings > Bluetooth and turn off Bluetooth. Then check the sound again.
Connect a headset. If you can hear sound through the headset, remove it and clear any dust or debris from the headset port on your device.
If your device is in a case, make sure that the case doesn’t block the speaker.
Use a brush to gently clear any debris from the speaker and Lightning connector (or 30-pin dock connector). The brush should have soft, clean, dry bristles.
Update your device to the latest version of iOS.
If you follow these steps and still hear no sound or distorted sound, contact Apple Support.
Over the course of the past few days, a handful of complaints have emerged on Apple’s support forum from iPhone 7 and iPhone 7 Plus owners claiming that they’re experiencing poor sound quality during phone calls.
“It’s like the phone is hollow and the sound is coming from behind it, ” writes a user describing the problem to a Community Specialist on the forum. He then goes on to add that the issue only occurs in calls.
Lowering the volume appears to alleviate the problem, but it’s certainly not a permanent fix. Fortunately, it looks like Apple is aware of the issue as it’s reportedly providing replacements to customers with a faulty handset.
It’s currently unclear whether the glitch is hardware- or software-related. I’m guessing that it’s to do with the former, though, If the issue was caused by a fault in iOS, it would almost certainly be widespread.
This news comes less than a week after Apple acknowledged and promised to patch a software bug on the iPhone 7 that renders the integrated remote on the newLightning EarPods useless.