Chug chug metal?!
Question: what is it?
Answers: what is it?
"Chugging" is a reference to the sound of the guitars. Playing with palm muted, generally slower rhythmic patterns produces a sort of Chug sound, like an old train going slow.
If I can find you an example to listen to of a chugging rhythm, I'll let you know. The only song I can think of right off the top of my head that has a chugging rhythm in parts is "Number Cruncher" by 'Destroyer Destroyer'. However that's just off the top of my head...