A workmate has had P0018 for the last 12 months on his VE series 2 Omega LFW over 250,000kms, had no chain work done for the last 10 years since he has owned it. Start the car and clear codes, can drive for hours until stopping engine, next start it shows P0018 again. No noises.
Last year I did look at the sensors and swapped between intake / exhaust on the drivers side, no change.
Have also removed and checked VVT solenoids. Applied some volts and cleaned with brake cleaner, no change.
He was going to take it to an auto electrician late last year, but is not too worried about it.