Removing Hum

Quick question.
I have an annoying hum SOMETIMES, but if I shake the cables, it goes away. Other times, it won't go away. One day my setup is whisper quiet, other days the system is hummin' with nothing turned on (except the mixer and the amplifier.)
What is the cause of this? My setup is super simple. MPC, turntable, mixer. Turntable is securely grounded. I've disconnected everything and the hum is still there. I have decent wires, but their not gold plated. I was told that this could be a problem, but I find that hard to believe since this is an occasional issue.
Anyone experienced this?

Is your amp grounded? Do you have anything crazy plugged in on the same circuit that the amp is on? I had a freezer in my basement that caused a high pitched whistle through my whole setup until I moved or unplugged that godforsaken thing!

I had the hum issue too for a while. It was because I wired the speaker wire incorrectly into the amp, I had the positive going into the negative and vice-versa, since I rewired it its quiet as a mouse. Also if your turntable has a switch to change from phono to line then switch it to line because phono tends to catch everything around in the studio and hums and bass-like warping effects will build up.

And crossing your input and output cables with the AC cable can cause that too. I read once that connecting your gear to the same outlet can eliminate hum too.

ground loop hum.

Thats interesting. Ok. I'm going to try all those suggestions. Right now, everything is quiet, but I had no idea the speaker wires has to be connected correctly. I mean, I usually just hook up the wires any ol way! haha!
Thanks for the help peeps. I'll post an update later this week or so.