Hi, hoping someone might be able to advise please...

my 2012 Insignia 2.0 CDTI has the NAVI 600 unit. It appears to work (sometimes get sniffy with the Satnav SD card and USB) but ...
when I'm on a call via the bluetooth connection the other person gets a lot of interference, which I don't hear - my end is fine. The interference also appears to be worse the faster the engine is running.
Thanks for any advice you can give.