So I installed a sub and woofers in mY 05 rx8.

I used a line out converter spliced into the left rear deck 6x9.

I then installed the aux in audio mod to stream spotify.

Now everything works fine until I plugin my phone to the lighter charger. After that I get a quiet whine with rpms,
But the audio sounds much louder and the bass is much cleaner.

If someone may know would a ground loop isolator work in my situation. And if so where would I put it as the whine comes from every speaker?

Thanks for all the help so far from the community.
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try running a ground wire from a screw on the chassis of your head unit to a bolt that goes into bare metal (i found good spot by removing glove box, bolt should not be used as ground for any other wires).