Q: iPhone 6s crackling when using bluetooth

Hello there Wire1981,

Thanks so much for joining us at the Apple Support Communities. I love listening to music from my iPhone in the car too, and crackling audio would definitely ruin the moment.  I have a  few things we can try to resolve the issue.

First of all, have you tried connecting your iPhone to other Bluetooth devices?  Do you notice crackling in the audio there as well?  Do you have another Bluetooth device you could try testing with your car to see if the crackling persists?    

Let's start off with an article that walks you through setting up your iPhone with a Bluetooth device:

Get help connecting a Bluetooth accessory with your iPhone, iPad, or iPod touch

You can try setting it up with Bluetooth headphones or speakers and test to see whether you notice the audio crackling there.  Once you've followed that article to test the audio on another Bluetooth device, we can set it up with the car again.  You may want to remove the Bluetooth Profile that's currently on there by going to:

Settings > Bluetooth > and then under MY DEVICES tap on the (i) and tap on Forget This Device.  Then follow the instructions below:

Get help connecting your iPhone, iPad, or iPod touch with your car stereo

Best wishes and hope your day is awesome!