Crackling is a different symptom from muffled or quiet sound -- it usually points to something physically interfering with the speaker's movement, rather than sound simply being blocked.
Volume Pushed Too High
At or near maximum volume, some speakers distort because the driver is being pushed past what it can move cleanly, especially on bass-heavy audio. Lower the volume a bit and see if the crackling clears -- if it does, this was the cause, not a fault.
Debris Against the Cone
Sand, dust or lint sitting directly against the speaker cone can vibrate and rattle as the cone moves, producing a crackling or buzzing sound that comes and goes with the audio. Dust Cleaner's sweeping tone is intended for exactly this kind of light, loose debris.
Moisture Around the Voice Coil
Crackling that started right after water exposure can mean moisture is interfering with the voice coil's movement rather than just muffling sound. Try Water Eject and give it time to fully dry between attempts.
A Loose Physical Connection
On some devices, especially laptops and external speakers, crackling can come from a loose internal cable or connector rather than the speaker itself -- this is more likely if the crackling changes when you move or flex the device, and it isn't something a sound-based tool can address.
Driver Damage
A torn cone or damaged voice coil can crackle constantly regardless of volume or content, often alongside a burning or rattling quality. If crackling persists after checking volume, debris and moisture, and especially after a drop or serious water exposure, the driver itself is the likely cause.
Narrowing It Down
Use Speaker Test with a steady tone -- if the crackling happens even on a clean, moderate-volume test tone, that rules out your original audio content as the cause and points more strongly toward debris, moisture or damage.