First, sound is perceived when things bump around in your ear, which is generally caused by air bumping around.
Moving your pick through the air therefore causes sound, and striking the strings is amplified by the guitar, creating even more sound.
Thus, pick sounds are unavoidable.
That said, there are various things you can do to lessen the sound.
One is your type of pick.
A harder, thicker pick will create more sound, so you could choose a thinner and/or softer one.
(As Lennart notes below, the opposite may be true for acoustic guitar.
It also depends how you play.
Picks are cheap, so get a few and experiment!)
You can also hold the pick more loosely, so that your fingers absorb some of the impact when the pick hits the strings.
Picking on an angle and drawing the pick across the strings will also create more pick sounds; the less the pick is in contact with the strings, the less sound it makes.
And of course, you can just play softer.
Don't hit the strings so hard :
P.
On the other hand, the behavior you describe in the question comments is caused by striking too softly or not following through.
You want a smooth, continuous motion through the strings.
While it's impossible to avoid entirely, try to avoid the inconsistent motion caused by the strings impeding your strumming.
This just takes practice, and a strong wrist.
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It sounds like you're playing chords by plucking strings one at a time.
Unless you're playing arpeggios, that's not the best way to do it:
Try strumming them all in a row, in a fluid motion.
Keep in mind that some pick noise is inevitable, even desirable.
In the studio, I do everything I can to emphasize incidental noises like the pick hitting the strings, the noises made by the flautist clicking the keys, or the vocalist inhaling before singing a line.
It's what makes music sound human and relatable.
Unless you're getting a truly horrifically loud series of clicks when playing, don't worry about it too much.
Listen to other players, and you'll hear that, to a point, this is normal and natural.
However, lighter nylon picks (like the ones put out by Clayton, for example) can mitigate this, as can lighter strings (although those would reduce the volume the strings produce, I think).
There are also hybrid silk/steel strings that can give you a softer sound.
(I'm guessing you're playing guitar with steel strings; classical guitars with nylon strings are generally not played with a plectrum.)
Like Matthew wrote in his answer , hold the pick more softly and play more gently and subtly.
You'll have a better dynamic range, a less percussive sound, and you'll have better control over your instrument.
You also ask about playing without a pick.
Sure, you can do that, but you'll be playing what's known as fingerstyle playing, a very different sort of music than strummed guitar.
You'll also be wearing down the fingernails on your strumming hand, so you'll want to prepare for that.
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Beyond what is said, there's pick angle.
I tend to get more of the click when I play with the pick hitting parallel to the string, so I try to hit with a little bit of an angle.
Another trick is compression.
My Boss CS3 has knobs for attack and sustain, and by turning down the attack, you'll control that picky pop a little.
Plus, of course, legato.
There's lots that'll tell you more here, including listening to Satriani, but in a nutshell, if you pick once and do lots with hammer-ons and pull offs, you will get a much smoother attack with little of the pick sound.
But, even with these techniques, you want to play around, try to get dynamics.
The pick sound can give an edge that you want for some songs.
music.stackexchange.com/users/195/Dave Jacoby
About 10 years ago I was obsessed with this very same question.
There are lots of things to try.
Go fingerstyle.
Don't be afraid!
Give it a go.
If your friends give you grief, make 'em watch Crossroads , already!
Beyond fingerstyle is the apoyando stroke.
Learn the rest stroke , where your fingertip grazes the string before the nail hits it and comes to rest on the next string.
This is the key to that sweet, sweet sound.
Try plucking closer to the middle of the string (away from the bridge).
But there's a beyond that, too.
For want of a better name, let's call it the Albert King soft-shoe .
After you can do an apoyando with the thumb, Do a strum with the thumb!
If you "brush" the strings with the flesh (no nail) of your fingers, you can summon sounds from the strings with almost zero attack .
It almost sounds like a synthesized clarinet.
I use Thomastik Nickel Flats in an obscenely heavy gauge.
This cuts even more exraneous upper harmonics (while paradoxically making it easier to play harmonics).
And the flat wrapping means I can play slides all the way across the neck with none of that scritcha-scratcha noise.
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Accuracy!
When I play a chord, after my pick triggers one string it then falls against the next string causing a clashing noise which kind of irritates me.
If you want to avoid that sound, you should avoid your pick hitting that final string.
Either by stopping the pick before it reaches the unwanted string, or by lifting your picking hand away from the strings, so the pick passes over the unwanted string without touching it.
Practice this slowly, then gradually work up your speed.
Precise plectrum work requires a lot of practice, but it's essential for many styles of playing.
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When I play the guitar (electric with steel strings), I can hear the noise of the pick clashing against the steel strings.  When I play a chord, after my pick triggers one string it then falls against the next string causing a clashing noise which kind of irritates me. Can I use the pick without that noise or should I play chords with my hands instead?  Is it the pick, my technique of holding the pick or does it have something to do with how I strike?
How can I prevent the noise my guitar pick makes?
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<electric-guitar><noise><picks>
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music.stackexchange.com/users/297/Tamara Wijsman
Playing with fingers avoids the problem of pick noise on the guitar. Otherwise, go for a lighter nylon pick and hold the pick more loosely and play more gently. Avoiding pick noise takes practice and a strong wrist.  Experiment with picks. A heavier pick may make more sound than a light one. Experiment with how you hold the pick and hold it more gently. Practice picking and strumming more smoothly. Develop accuracy. Experiment with fingerstyle playing - without a pick.
Experiment with picks. A heavier pick may make more sound than a light one. Accuracy. Experiment with how you hold the pick and hold it more gently. Practice picking and strumming more smoothly. Experiment with fingerstyle playing - without a pick.