Stop high frequency noise from iPhone dock's line out in car adapter I am running an iPhone 4S through a Griffin TuneFlex 9865. After just discovering the line out jack I have helped uncovered another problem. Now, while then engine is on there is a high frequency buzz aka alternator whine, that varies pitch based on the engine RPM. Are there anyways to stop the high frequency noise, or at least reduce it. I  think my volume level is quite low from the line out, and is requiring me to turn the radio volume up much louder near maximum, which might be revealing the issue. How can I fix this? Do I need an amplifier?
You're discovering the joys of noisy electrical grids in cars.


  Do I need an amplifier?


Nope. You need a filter.

And filtering noisy car electricity is...tricky. You can't just create new, separate paths to ground because there aren't a lot of choices for where ground is in a car.

You can try putting a simple choke filter on the line between your player and the input to the stereo. That's the cheapest and easiest way to try and fix the problem. Something like this is sufficient.

If that doesn't cut the noisy you need to filter the power. Finding one of those car DC to AC inverters with a built-in USB port is likely your best bet. Something like this is what I'd suggest you try if the choke doesn't help.