Q: how will i remove the crackling sounds when i using loudspeaker?

Hello there, frences08.

The following Knowledge Base article offers up some great steps for troubleshooting the issue you seem to be describing:

iPhone: No sound or distorted sound from speaker

http://support.apple.com/kb/ts5180

1. Verify that the volume is set to a level you would normally be able to hear.
2. Ensure that there is nothing plugged in to the headset jack or the dock connector.
3. If the iPhone is in a protective case, make sure that the speaker port isn't blocked by the case.
4. Make sure that the speaker and dock port aren't clogged with debris. If necessary, clean it with a clean, small, dry, soft-bristled brush. Carefully and gently brush away any debris.
5. If an audio issue occurs when using a specific application, try testing other applications to see if the issue persists.
6. If the iPhone is paired with a Bluetooth headset or car kit:
   • Try turning off Bluetooth.
   • If you experience difficulties with the Bluetooth feature, follow these troubleshooting steps.
7. Restart the iPhone.
8. If restarting doesn't fix the issue, ensure that your iPhone is updated to the latest version of iOS.
9. If the issue is not resolved, please  contact Apple Support.

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro.