You can get different tones through palm muting. Palm muting closer to the bridge lets the notes ring through better. Palm muting closer to the neck makes it sound more like a *clunk* noise... where the notes don't come through as well. I generally play with my strat in the 4th switch position (activating the middle and bridge pickups)... and I usually palm mute either between the middle and bridge pickups... or directly over the bridge pickup. Experiment with that and see what sounds best for you. Don't be afraid to push down a little on the strings with your palm either. The harder you press the more it will mute the notes. Since you have a humbucker in the bridge, your palm muting would probably sound the best when you activate the humbucker and palm mute over the top of it or just slightly the the bridge side of it. Different people do it different ways. Just find what works for you.