Tried a couple of system apps as advised...
Google launcher: couldn't access the basic settings, couldn't remove the Google search widget, it looks like bundled with network services - not good, back to Nova.
Viper v4a equaliser: it requests unnecessary permissions to access literary everything, rings home to China, and it is bloated with unnecessary features, back to DSP manager.
Further ROM testing. When making a hands-free call in the car, the screen lights and shows the usual call controls. These can be activated by accidentally touching the screen. If the call is started on hands-free, but interrupted from the screen, Bluetooth hangs and takes a lot of fiddling to recover. Receiving calls on hands-free, while the phone is in the pocket is buggy - possibly related to the above problem. Will investigate this further when have time.