Yep you can use midi to make drum loops, I have done it in Sonar, so I imagine you can do it in cubase or what ever is bundles with the GNX4.

Can you get rid of the noise with a gate program ? There is bound to be a noise suppressor built into the the GNX4, just turn the threshold down a bit so it kicks in when you are not playing anything.

As far as the shocking is concerned, Id have that checked out as it is not good. if all your stuff is grounded you may want to check the ground on the plug with a line tester. One of these little gizmo's can save your life. If you are playing gigs regularly, they are a very good idea to carry round with you !!!