I have also had this problem through the AUX input.   Not only that, when I play music through Chromecast audio the quality is very low Fidelity. I have tried replacing the 3.5 mm cord with little success. Is that input just low fidelity or is there another problem?   The Bluetooth signal and the sound quality are far superior than 3.5 mm input. Any thoughts would be appreciated. 

Which source and OS are you using?

In case of Android you can try installing Bubbleupnp and playing  your music from here.

You will need to activate "automatically transcoding" before!

If it all works flawlessly (mostly the sound is better too) and the music stops like it should, you will know that it's a faulty implementation of Chromecast by your streaming service. Had the same thing with Qobuz for a week or so, reported it to Qobuz customer service and they fixed it quickly.

If Bubbleupnp doesn't work, this must be an issue with B&O software and should be reported to B&O customer service.

 Thanks for taking the time to post this. I’m using Apple iOS. I spent a couple of hours with Google and they were able to show me that their device is working properly. I’ve been had bang and Olufsen’s service department get on the line and they had me reset the software back to factory default on the Beolit 15. It didn’t really solve the problem, but the music sounds a little bit better. Still pretty muddy and the high ranges are not what they should be. I think I’m just going to wind up living with it. 

New question on the same topic. AirPlay two has now come out. The fidelity is a lot better and it is much more stable. How do I get an airplay two signal into my Beolit 15? Do I need to get an older Apple airport express second generation? What is the best way?