Why does my vape crackle?

Can you explain to me, in simple terms, why my vape is making a crackling sound? I've tried cleaning it and changing the coils, but the issue persists. Could it be due to the type of e-liquid I'm using, or is it a sign of a more serious issue with the device? I'm not very knowledgeable about vaping, so any information you can provide would be greatly appreciated.