So I had done pretty much everything that could be done to remove a slightly (very minimal, but audible) whine from my car system. I grounded, isolated, etc. etc.
Then i got an ad for a device called the iMic USB audio adapter.
This little thing takes audio out through USB and renders it out to a mini plug. WOW!!
The whine went away and I swear it sounds cleaner!!
I'm so blown away. I have louder levels and cleaner sound. I don't work for them, but this is amazing.
web page
another similar device:
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Check them out!!