Dissimilation
When a sound becomes less like the surrounding letters.
Metathesis
Reorders a sequence of segments. i.e., cavalry becomes calvary
Deletion
Removes a segment from a word. Pronouncing twenny, rather than twenty.
Epenthesis
Process of inserting a segment into a particular environment to help with production and articulation. i.e., athlete [ǽ θ l ì t ̚] becomes [ǽ θ ə l ì t ̚]