One frequent source of signal noise is a loose or worn output jack. They can become loose in two ways. The first way the output jack can cause signal noise is in the mounting to the body of the guitar. This does not always cause significant noise, but it can cause more damage to the guitar and the output jack over the long run. If it is loose in it's mount to the body of the guitar, any movement and work soldering loose or cause shorts in the wires.
The second, and primary cause of signal noise, is when the internal components of the output jack. Generally, this is only a problem with the type of jacks that are pictured. What happens is the internal contact that acts with a type of spring loaded tension simply looses tension. All you have to do is access the jack and carefully bend the contact toward the center of the component. This generally resolves an issue caused by a loose contact.