If the sound is muffled, get to the front of the speaker and check for powdered iron or iron filings. If you're in an environment where there's some finely powdered iron in the air, it can become attracted to the speaker magnet, from the cone side, and press the cone against the magnet, muffling the sound. (An environment like downtown where a new building is going up.)
You can use a tny screwdriver to pick up all that iron junk and the speaker will be as good as new.
OTOH, if the scanner was in hot dry places, the cone may have dried out, causing a different kind of distortion. The only remedy for that is replacing the speaker, but it's simple. At most the speaker is held in by 2 screwed-in clamps and a bead of rubber cement (or some harder glue). Unsolder the 2 leads, free the speaker, put in the new one and resolder the leads. (It doesn't matter which lead goes to which terminal.) And, if you can find a better quality speaker in the same size and impedance, you're ahead of the game.
