rest your pick hand on the bridge while playing, it sounds like chuga-chuga. oyu canb get a similar sound by resting your finger over the frets instead of pushing down on them, but thats a harmonic and might not give you the sound you want
Palm muting is basically what these other guys have already described, and it takes some time before it feels comfortable, but after a while of practicing (especially if the majority of the things you are playing contain PMing), you will be able to PM at any given time and add a completly new variation and sound to your playing.

PMing is a great, and in some cases, a necessary technique to master, so practice practice practice .
Got a question about Baritone guitars? Feel free to PM me.

Thanks to UG, I converted from Metalcore to some "real" Metal.
everyone else is right above me, you can palm mute more or less though, for less, rest your hand closer to bridge, for more... further away.