Radio/Stereo: HU-850 problems

[Beeleyflyer]

I hope I am doing this right as I am a new user.

Just bought a 2004 XC70 2.4D5 Lux AWD with SatNav and integrated phone. Radio head unit is HU-850. At first radio worked fine but now FM keeps cutting out and then after a while back in again. Sometimes sound comes back partially. While this is going on I can use AM, CD, Sat Nav and phone without problem.
Only adaption is have a plug Bluetooth adapter plugged into the 12v socket on dash which connects to the radio via an FM transmitter to an unused frequency.

Any one else experienced this or have idea what is the problem or how to fix?

Also in Dolby mode hardly any sound from rear speakers but seems ok in 3 channel or 'OFF' position.

Any help appreciated.