I'm noodling on my newly acquired Classic Vibe Bass VI and I'm playing it through my Fender Mustang GTX100 amp rather than a bass amp so I can make use of some of the lovely fx. I am getting a fair amount of electrical noise which goes away when I touch the control plate, but stays at the same level if I only touch the strings, bridge or vibrato unit. Is there likely to be a loose/missing ground wire?