A Different Kind Of Ground Buzz Problem

[Nox]

@SSS Yes, i tried with 5 different guitar cables.

@AnalogSteph When I plug in the studio monitors while the notebook is running on battery power, the closed circuit I mentioned earlier breaks and the noise starts. My house was built 6 years ago. Is there any way for me to check the PE?

 

[Blumlein 88]

I don't know if this is your problem. As it has that hum/buzz with the guitar disconnected. A friend had a Japanese copy of a Les Paul from sometime in the 1980s. He had a very similar buzz. He had a magazine article somewhere detailing how with time some caps inside would go bad and cause this. He had me replace the caps and that fixed the problem. That was like 15 years ago so I don't remember the details. It too would stop buzzing if you touched metal on the guitar.

Seems like they were tantalum caps and I found some mylars I could fit in the space.

 

[AnalogSteph]

@AnalogSteph When I plug in the studio monitors while the notebook is running on battery power, the closed circuit I mentioned earlier breaks and the noise starts. My house was built 6 years ago. Is there any way for me to check the PE?

Possibly, but you'll need a multimeter with a lowish-voltage AC range. Measure the AC voltage between the outlet's ground terminal and yourself. Going around my apartment, I'm seeing between about 0.7 and 2-3 V, so that range seems to be normal. Leaning against the wall near some of them seems to increase the value, so maybe I'm coupling to the power wires there. (I've never thought about potential gradients inside my walls before, but it's certainly possible. Around here you have the wires laid into massive brick or concrete walls without much of any conduit to speak of..)

 

[Speedskater]

That's just what electricians call 'phantom voltage' when measured with a modern high impedance DMM multi-meter.
If you use an old-fashioned analog meter with a moving needle scale, the value would be much lower.

Find a friendly electrician, with a sensitive current probe.
Have him measure the current at the breaker box, with everything turned off of the Hot & Neutral wires.
It should be under 1/4 Amp on each with.
Then measure with lots of things turned on.
The Hot & Neutral should have equal readings.