I know there are various threads on this, which I have looked into, and there is a general feeling, and indeed some experience, to suggest that it tends to be an o-ring problem if the solenoids seem to be working ok.

I have my engine front cover off at the moment and looking at a tick in one bank. What happens in general terms is that after some time idling the right bank ticks loudly. If I rev the engine the solenoids fire and the ticking disappears as oil flows into the vvt device. Then, after some minutes further idling, the ticking returns. I think this is a fairly typical experience?

Having looked into how the system functions, and looking at the vvt carrier that the oil flows through, I am a little bemused by what happens. As I understand it, at a certain rpm the solenoid fires, oil flows into the vvt unit, compressing the spring and changing the timing through the helical gear. Then, when the revs drop, the solenoid deactivates and the oil flows out of the vvt unit, releasing the spring etc, etc.

If that's the case, why does the ticking start some minutes later? What actually causes it, as the vvt unit should be empty of oil from the point at which the solenoid is deactivated? What happens in the time between the vvt solenoid deactivating and the ticking starting?