Bluetooth audio issues with BMW

I have an iPhone 6 and a 5 both running iOS11.1.1 and now the bluetooth streaming audio stutters and cuts out, the song then speeds up to make sure the run time is correct, very annoying and makes using my phone to listen to music impossible.

Wifes iPhone 6 running iOS 10.3.3 doesnt have this issue, the BMW is a 2013 model with the updated software.

anyone got a solution?

Ive tried unparing and deleting the phones but makes no difference.