Hissing noise in car with iPhone X

Hi guys! Just updated from the 6S Plus to the iPhone X and everything is pretty great - however I have an issue with playing music (via Spotify) in my car. I believe this is an issue with others playing music even back to the iPhone 7.

Previously with my 6S, I connected it to my car via an AUX-to-AUX cable. No issues whatsoever. I tried it since getting the X with the same cable, but with the AUX-to-lightning adapter, and I get an intermittent hissing noise. I realise that this is when there is a change in the frequency of the song almost, for eg changing songs, or when the song goes from a louder/higher pitch to a softer one. This change brings out a hiss for about 5-6 seconds.

Now I'm pretty sure it is not a problem with the phone itself.

1) Phone speaker playback is fine.

2) I've tried using my Sony Bluetooth headphones - no problems.

3) I've even tried using the adapter with my Fidelio in-ear buds and it doesn't reproduce any interference!

I'm going to purchase an AUX-to-lightning cable for the car, to bypass the adapter, and try it that way.

Anyone else with any suggestions??