Sound Fades Left to Right and Back at High Volume

A guy I know installed a subwoofer amplifier and sub in his 2017 Equinox.For signal he tapped the front low levels before they entered the stock amp.Obviously he left all the connectors in the stock amp as he was just adding a sub to the system.Now the issue is that when he cranks it at high volumes the sound goes back and forth between the left and right speakers as if somebody is rapidly turning the balance knob left and right and left and right,etc.

Anybody got a clue as to what could be causing this bizarre issue?

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Rumors of Bob but never Bob......So what is it you tell people you do these days Bob?

This may or may not be related.

Did he just connect some RCA's to the speaker leads? If so, the outer conductor of the RCA's is an audio ground for the amplifier. This means the speaker leads are effectively being grounded.

Things to try would be using an audio isolation transformer/ground loop isolator. Another option would be to disconnect the leads that are connected to the outer RCA conductors.

You could try high level inputs or a line out converter as well.

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My ex once told me I have a perfect face for radio.

Thanks for the reply.It wasn't the speaker leads that he attached RCA's to,it was the stock low level audio signal that he attached them to.Then ran those RCA's to his RCA inputs at the aftermarket amp.

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Rumors of Bob but never Bob......So what is it you tell people you do these days Bob?

I was using the wrong terminology, but unless the factory low level wires have continuity to ground, it still may be the issue.

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My ex once told me I have a perfect face for radio.

Use a line out converter on the output side of the factory amplifier. If his sub amplifier does not have balanced inputs (which most don't) the shields of the amplifier are connected together. Thus connecting the left and right negatives together. Obviously the radio does not like this situation.

That's interesting,there is only a + and - wire on the stock low levels though.Don't balanced signals have 3 wires?Also,do you think a LOC on the low levels would fix it?Thanks for the insights!

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Rumors of Bob but never Bob......So what is it you tell people you do these days Bob?

I know a line out converter will fix the problem.

I understand putting a line out converter on the outputs after the amplifier will work but what I'm asking you is will putting a line out converter on the low level inputs before they enter the stock amp, will that work?

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Rumors of Bob but never Bob......So what is it you tell people you do these days Bob?

You don't want to put a line out converter on the low level. That would likely attenuate the signal too much, since it is already a low level.

But along the same line of reasoning, you could simply try an audio isolation transformer/ground loop isolator (PAC SNI-1) without further modifications.

You could also only connect one low level lead per side (either both positive, or both negative) to the inner conductor of the RCA's and no low level lead to the outer conductor. You could actually ground the outer conductor if you do this.

Your third option would be as IAAI recommended, to connect a line out converter to the speaker leads.

If the amp has high level inputs, you could try those as well.

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My ex once told me I have a perfect face for radio.

you can try grounding the shields of the RCA cable going to the amplifier and connect only the center conductor of the RCAs to the positive signal wires of the amplifier input wires. Connect nothing to the negative signal wires.

Thanks for the input guys, seriously.I wish I understood the intricacies of balanced and unbalanced signals and inputs,etc.It's sort of confusing to me this far even as much as I've studied it.

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Rumors of Bob but never Bob......So what is it you tell people you do these days Bob?