This palm-mute accent pattern creates a polyrhythmic sound. Because you don't palm-mute the first 16th note of every grouping of three 16th notes, four times you create an emphasis with the chords that are evenly spaced across three beats. Beat four is when the polyrhythm is no longer happening.
Here is the Guitar Pro 6 tab for this lesson:
HEY!!! Does Your Rhythm SUCK!?