"Muffled" is a symptom, not a diagnosis -- and it can come from several unrelated causes. Working through them roughly in order of how common (and how easy to fix) they are will save you time.
1. Check the obvious physical blockers first
A phone case, screen protector overhang, or a pocket lining pressed against the speaker grille can muffle sound just by physically covering part of the opening. Remove the case and test again before assuming there's an internal problem.
2. Check your audio settings
Equalizer settings, a "media volume limiter," Bluetooth codec quality, or an accessibility audio setting (like mono audio or balance skewed to one side) can all make sound seem duller or quieter than expected. This is especially worth checking if the muffling happened right after a software update or after connecting a new Bluetooth device.
3. Rule out debris
Pocket lint, sand, or general dust buildup in the speaker grille is one of the most common physical causes of muffled sound, especially on phones. It typically comes on gradually rather than suddenly. Try the Dust Cleaner tool, which uses a sweeping tone designed to loosen this kind of light debris.
4. Rule out moisture
If the muffling appeared suddenly after a splash, being caught in rain, or a drop near water, moisture trapped in the speaker mesh is the likely cause. Try Water Eject, which uses a low, pulsing tone to help move trapped water out.
5. Test both channels independently
Muffling that's actually worse on one side can be mistaken for general muffling. Use Speaker Test to listen to left, right and both channels separately -- if one side is clearly worse, that narrows the problem to a specific speaker rather than a general setting.
6. Consider hardware damage
If you've ruled out a case, settings, debris and moisture, and sound is still muffled or distorted, the cause is likely a damaged speaker driver or component -- something no cleaning tool can fix. This is more likely if the phone has been dropped, exposed to significant water, or is simply old.
Not sure where to start?
Use the Muffled Sound option in the tool selector on our homepage -- it asks a couple of quick questions and points you to the right tool.