When my car kit was first fitted and I got a call it rang through the car audio system. After a while it stopped doing this and now when in the cradle it rings through the handset and also asks me if I want to divert the call to the handset which it didn't do when first installed. I can obviously hear the call through the audio system, but not the ring.

It must be something I've done, how do I get it back to ringing through the audio system?