Why the Hell...

[Cicero]

This is a grounding adapter. Be advised.
http://www.radioshack.com/product/in...ductId=2104010

[Elspode]

Power supplies on both computers are plugged into a grounded plugstrip which is in turn plugged into a grounded outlet. So the system is grounded. The only other connection is from each computer's headphone out jack to L/R line ins on a receiver/amp.

I have also bypassed the plug strip and plugged the computers directly into the wall socket with the same result. In reading up, ground loops aer not completely unknown, hence, the existence of the device I posted. I am quite familiar with 60 cycle hum in audio gear. DI boxes, for example, usually have a 'ground lift' setting, and other audio gear, such as mixer boards, usually have a polarity invert switch which does essentially the same thing.

I'm just kinda baffled why it is happening in two separate laptops, yet does not occur in anything else which comprises the audio path (stereo, tv, etc).

[tw]

Originally Posted by Elspode

Power supplies on both computers are plugged into a grounded plugstrip which is in turn plugged into a grounded outlet. So the system is grounded. The only other connection is from each computer's headphone out jack to L/R line ins on a receiver/amp.

I have also bypassed the plug strip and plugged the computers directly into the wall socket with the same result.

So you have speculated that the computer is grounded. OK. That is the hypothesis. Now, where is your experimental evidence that is also required before a fact can exist. Nothing yet says the system is grounded.

Requested were a few experiments in the previous post. Without experiment results, then nobody knows that the system is grounded.

Meanwhile you have a receiver/amp that you did not mention? The sentence is vague. Is the computer headphone wires (both left and right) connected to the input of a receiver amp? Is it the same receiver amp that makes a hum for both computers? Does this amp also have the necessary three prong plug? Where is this amp powered?

Rationing facts does not help with the diagnosis. Because you hope the receptacle is a ground (and you don't say which type of ground) does not mean anything is actually grounded.

If the Radio Shack isolator does something between a computer headphone jack and the power amp, then something is defective in one of those two items (more probably the amplifier) OR a wiring problem exists.

Currently everything is only speculation because none of the experiments have been performed and suddenly new facts such as the amplifier are discovered. Nothing connected to any USB port? No network or modem cable? Is that an RCA jack connection to amp input from headphone output? With numerous AC power connections, the system is more complex meaning the three prong to two prong experiment must be performed for each item singly and all other permutations. And testing the entire system in another building remains useful information.