All Audio related functions only work sometimes at random

[PNick]

Hi, I have a 2016 CT200H. When I start up the audio does not come on - I get a ticking sound. 

SatNav works on the display, but no audio.

Voice command does not work

UNTIL suddenly it will wake up and start working. Might be 5 mins, might be 30 mins, no consistent response. Once it starts working typically the SatNav will kick in and tell me that directions will start from wherever I actually am at that moment, and then works until arrival. From that point on voice command will work - in as much as it ever was functional anyway.

All is fine until either you turn off the audio or the car, after which you have the same random wait again.

I've seen a number of threads with different audio issues, but none that seem like this. Has anyone come across this or could give me some advice - preferably not including volunteering to spend huge amounts of money at a Lexus main dealer.