My Marshall's MG100HCFX has been having some issues. Every time I turn it own it has a constant low hum than never changes no mater what I do, ive run multiple guitars theough it, through my pedals and without my pedals, and ive changed every setting on the amp, guitar, and pedals and nothings changed. I can even take the cable out of the output jack and nothing will change. However if i jiggle the cable connecting the head to the cab, then and only then will the noise change from low hum to static. Video demonstrates what happens when I turn the amp on.