Cd30 astra?

Ok, here goes.
Keys in the ignition switched on (before engine) radio comes on nice and crystal. Switch ignition on, radio goes to a quite hash sound then silence.
Ignition off and no change.
Wait a day or two and the cycle restarts. Really is bizarre.
Checked all wiring and looks good. However back speakers don’t work?? Perhaps a connection problem .. but how would the cycle work of the problem is there.