The iphone 5 has built in speakers, which allow you to use them for music and video playback. They provide decent sound quality for what they are, but you could connect an external speaker dock for better sound quality and louder volume. If you constantly use the speakers on your iphone5 daily, it is very likely that dust and dirt particles have gotten their way into the vents. Once this happens, every time you use the speakers for audio playback, the dirt and dust on the speakers will vibrate, making a crackling sound to be heard. Usually, this type of sound problem can be resolved by cleaning the grills covering up the speakers.
1) On the iphone5 model, the speakers are located at the bottom of the mobile phone, next to the charging socket.
2) Now that you have located them, obtain a can of Compress Air. This can contains clean air pressure, which will help blast off all the dust and dirt blocking the speaker grills. This can be purchased from shops that sell computer parts. You could disassemble your iphone5 for an thorough clean, but this is a tricky procedure and will void your warranty.
3) Attach the plastic straw that comes supplied with the can of compress air. Then aim the straw towards the speaker grills and give the can a few blasts. To see if the crackle sound is disappeared, enable music playback on your handset. If it is improved slightly, then continue cleaning them out, with the can of compressed air. If you see no improvement at all, the speakers are blown and will need replacing with brand new ones.