My amp makes this static noise wich goes off as soon as i touch one of the strings or the metal part of the guitar cable. What can i do to make the noise disapear

Get inside it and check the connections to the plug especially any shielding / braiding. Resolder the connections.

Assuming that the problem goes away when you plug a differebt guitart into your amp, you have a loose ground somewhere in the guitar.

It is a definite pickup grounding issue causing hum/"buzz" which diminishes when touching strings. Check the impedance of cable jack inputs and cable which should be 1/4"mono input/output jacks) . A personal preference but effective is to NOT run guitar direct into mixer but through an external amp w/ a headphone out jack . Noise gating/preamp filter also will help eliminate the "buzz"/noise from pickups. It is unfortunately the nature of the "electro-magnetic" beast when it comes to electric guitar pickups .Hope this helps.

The internal workings of the guitar - pickups, potentiometers, switches are not grounded.
Very common.

you may have a ground loop problem and when you touch the strings you complete the ground loop so the noise dissapears. make sure the amp is plugged into a proper grounded outlet. also there is an aftermarket ground plate that goes under the pick guard. that is what I put on mine to cut the emf way down. if you bought the guitar from a dealer take it back to the store and ask them why you are getting so much noise.

All amps make a small amount of noise (system hiss) but the amps own power supply should not cause a problem on it's own.
However if the frequency is around 50hz (the G 2 1/2 octaves below middle C on a piano) it is most likely due mains electricity interference or an earth (grounding) issue.
Here are a few things to try to identify the source.

1. Could be a lack of earth (grounding) This is potentially VERY DANGEROUS and could result in electric shock if you touch a metal part of the amp or touch some other metal object (like a microphone stand at the same time as your guitar strings). Check the earth wire is firmly attached at both ends of the power supply lead.
2. Could be a defective mains socket - try plugging it in to a different one, preferably on a totally separate circuit.
3. Could be an earth loop. These can occur if you are using the amp with an output to a public address system or mixer that is also earthed because of a 'potential difference' between the two earths. Solution - use the balanced (xlr) output which incorporates an earth lift rather than the unbalanced jack output.
4. Unplug any effects pedals, foot-switch etcetera to see if that eliminates the problem. Turn off any internal effects, including bass intensifier.
5. Make sure any signal cables (guitar leads) have good quality screening and that the screen is well soldered to the jack plugs at both ends.
6. Ensure signal leads do not lay along side (parallel) close to mains electricity cables but are well separated and only cross at right angles.
7. Move the amp away form other electrical equipment that may have a powerful magnetic field (especially CD or DVD players, hearing loop amplifiers, radio microphone transmitters / receivers, mobile phones
8. Turn around or stand in a different position - it might simply be the pick-ups in your guitar causing interference in the magnetic field of the power supply.
9. Does plugging in or unplugging a signal lead / guitar make any difference? This particular amp requires only mono jack plugs a stereo (trs) plug may be shorting across terminals
10. Does it change when you touch the strings with your hand? If yes check internal wiring and screening within the guitar.

Have you tried another cable between amp and guitar? Usually the cable goes bad first. Have you tried another amp or possibly tried another guitar on your rig? If this still indicates that your guitar's Standard 1/4" TS Jack is noisy, remove the oval cover over the jack and check the solder joints for the wiring. Follow the wires back to the tone and volume pots and check those solder joints. If everything is secure...Plug in, power up and check for noise while turning the volume pots stop to stop. If the pots make a scratching noise, shut down rig and unplug the guitar. Get a can of spray contact cleaner with a small extension tube (available at electronic shops) to spray in the pots while turning them. (May have to remove pots fom the guitar to get at small openings on side of pot can.) Spray jack and test for noise. Jack STILL
noisy...If you can solder...unwire old jack, remove from guitar, take to electronic shop, match to Standard 1/4" TS Jack, install in guitar, resolder wire connections and test. If you cannot solder...take guitar to
a reputable shop or dealer that does this repair. Good Luck! P.S. The
spray contact cleaner can be used on the amp jack, pots and switches
too...just make sure the amp is unplugged from the power supply before
doing any spraying.

Just a thought:

If you used the speakers with another amp and they still make noise when you play certain frequencies, then it is obviously a problem with the speakers or the cabinet - it could be a mechanical resonance in some part of a speaker / cabinet, something like a loose screw or a nut, loose protection mesh on the speakers that resonates at certain frequencies, possibly a bad speaker or a speaker membrane...

Also, you might want to check the pickups on your guitar, see if the pickup core slug under the A string is much closer to the string than the other slugs so it is either picking up too much signal and distorting it or the string might be touching the slug when you play it and cause noise, also see if the string is touching something else when it vibrates...

good luck

3rq8 (Triarcuate)

To me this is a natural reaction to having the volume all the way up, when you touch the strings your stopping any vibration from taking place there by stopping the static, or the other problem could be that your pickups are set up much to close to your strings, try to lower them and see what happens, a bad cord could also be the culprite.

This is a very common problem that I have repaired for many friends. Sometimes the guitar jack becomes loose and gets rotated to the point where the wire breaks and/or touches the cord plug when it's inserted into the jack. You need to remove the access plate/panel at the back of the guitar body and see if the wire is broke or twisted. You may only have to loosen the jack retaining nut and rotate the jack to get the twist out or you may have to remove the jack and resolder the wire back in place. If its broke make sure to solder back on the proper terminal--the one with solder already on it and not the one that the cord plug touches when its inserted. Retighten the jack nut by firmly holding the jack from access side so it doesn't rotate again and cause that undesirable STATIC sound. Hope this helps.