problem with cpx5 electrics

[stringbender uk]

hi can anyone help? my cpx 5 has a hum,which is very audible,but when i touch the metal on the end pin the hum goes away. has anyone had this problem before?any advice on what to replace would be welcome
my local shop has had the guitar for two weeks and done absolutely nothing!it goes to show the general lack of knowledge and experience of the staff most of these shops employ! they wanted £40 to send it to a "expert" to even look at it! so i thought id try and fix it with your help.after all it can hardly be rocket science!
many thanks JOHN