#1
I thought I'd eliminated all the unwanted sounds I could when playing with heavy distortion. However today, I decided I would flick my pickup swtich so I'd get a heavier sound. So I started playing the same old progressions again on distortion, and yet now, to my horror I keep getting loads of unwanted sounds, and I can't seem to stop them.

For example, when I am playing power chords, and after each chord putting my picking hand down on the strings to mute before changing chord, I get a harmonic kind of sound caused by the hand coming down. Or, I get the harmonic sound of my fretting hand coming off the strings, even though I mute with my picking hand straight away.

What can I do?
#2
Upping the amount of distortion you use is a surefire way to magnify the flaws in your playing - string noises and the like that go relatively unnoticed beforehand will suddenly become glaringly obvious, as I'm sure you just realized.

That said, when you have a lot of distortion sometimes the occasional noise can be near impossible to mute - but here are a few considerations...

- You could be muting the strings where natural harmonics occur (hence unintentionally playing them), try muting with your picking hand pretty much at the same place that you would palm mute (right near the bridge) - it can be more effective for deadening the string sound.

- Also, removing your fretting hand can cause noise at the best of times and with distortion often causes a pull-off to the open string to sound, and especially if you are removing your fingers with too much force. Try to gently lift them.

Both of these alone will help eliminate noise, but for best effect you should be muting both ways. Also, make sure when you mute with your right hand that you cover all the strings, even the ones you didn't play, so you don't get sympathetic string noise.

Combine gentle lifting of your fingers and muting near the bridge in a near simultaneous manner, and you'll find you will eliminate most noises.
Roberto Moretti - Author of 'Practice Made Perfect: How Anyone Can Master Anything Quicker, Easier and Better than Ever'