Strange hum coming out of Dual G4 2.5 Built-in Audio

So this problem is somewhat baffling to me. I've got a pretty thick studio cable with an 1/8" inch connection coming out of the Built-in Audio speaker jack in the back of my G4 going into a setup that feeds out to these big studio monitors.

When I start to turn up the volume coming out of the Built-in Audio connection on the mixer, a very noticeable hum is produced that does not occur by other devices or sound cards coming out the speakers. I switched out the cable with another cable and the same thing happened. Any ideas?

-Tim

are your studio monitors powered??? if they are is everything coming off of the sam branch circuit????

You most likely have a 60hz "ground Loop" hum being produced. Caused by the computer and the speakers being on different grounds.

My first suggestion would be to lift the ground on the speakers and see if that makes it happy. If not you may need to look into and isolation transformer to get rid of it.

The problem is that the hum being produced is NOT a constant hum, like an oscillator or anything.

More details on what I've done, for example, if I unplug the TT patch bay cables to the G4 the sound stops. Changing the power cord to a spare doesn't do anything to help. Putting the CPU on a different circuit branch doesn't help. I changed around the TT patch bay cables to see if the cables might be the cause, which didn't do anything. Still pretty baffled as to what it is.