This is another dumb newbie problem. I am using a small Peavey practice amp with a Ibanez BTB 515 and a cheap cable. With BTB volume and treble set at reasonable settings (say 9PM) and the Peavey at no more than 11AM, there is a very annoying hissing/buzzing sound that gets worse when no fingers are on any strings. Is this just a fact of life, or is something in my signal chain hosed? Peavy has a 3 prong plug, BTW.
Sounds like a bad ground to me. Plugging into a different outlet may help, but I'm not entirely sure. Do you have any other electrical devices nearby? I've found that lamps and TV's especially can make the hiss worse if they are on and the bass's pickups are pointing at them. Also, you might want to try lowering the treble a bit. Treble circuits do tend to be noisier in lower-end equipment.
Does it go away completly when you put you hand on any metal parts, like the bridge, strings, maybe tuners? If so, then either grounding or ahh **** I can't remember what the other thing is that it could be (so basically this help is of no use)...My local tech helped me out with this on my first Squire P...I'll try to remember what he said to do...