My Vox DA5 amp is just over a week old, and it makes a faint static noise whenever it is plugged in. It isn't very loud, but enough to irritate me. It does this even with no guitar/cable plugged in, and with all the knobs turned down to 0. I have tried it at different plugs around the house, and it is the same. It also makes several loud cracking noises when I turn it on. I am really new at this, so any help is much appreciated.