Roger pen/transmitter fading

I recently bought and have now just returned Roger pen transmitter and Mylink receiver with kneckloop because I cannot be sure there isn't a fault. While travelling in car or just sitting in queueing traffic,  the volume at my hearing aids keep going right down to the point where I can't hear anything at all. Then it either decideds to randomly come back up again on it's own or  my friend talks and it "wakes it up again. My friend said perhaps its some power saving feature but I think that would be ridiculous. When the volume level goes right down I feel obviously disorientated and cannot hardly hear any background noise,  I probably wouldn't even hear if someone beeped their horn. I tryed this kit in a busy restaurant with loud hubub and music playing and this didn't happen. I thought maybe it's the electronics in car interfering with the kit ,  although I don't have any extra equipment fitted. Had been in touch with customer services at Connevans but the chap was puzzled as to what it could be. Has anybody out there experienced this same problem with this kit