Today i installed a Sony WX-900BT in my VW Golf MKV. When playing the radio it plays absolutely fine sound wise, if not the fact that it's a fair bit quieter than the stock unit, Not sure if there is a way of changing that. But the bigger problem is when i try to play music through AUX or Bluetooth, the sound quality drops quite a bit, there's very noticeable crackling and it's not clean and crisp. That doesn't happen with the radio. The phone i'm using is an iPhone 6. It can't be the songs because i was playing them through Spotfy which has decent sound.