2003 Holden Ute load ticking noise

Hi guys, I have a load ticking noise in my engine! The sound is not there at start up but only after about a 5 minute drive the sound apears then when shut down and restarted the sound is gone, I thought it was the oil pump so I changed it but still the same problem, when the engine was open there was alot of sludge and burnt oil stuck all over the inside, the car isnt using oil, the sound is only on the right side of the engine so I opened the rocker cover to check the valves and springs once again alot of sludge and burnt oil stuck to everything I closed it back up and went for another drive this time no noise at all I left it to idle for 20minutes only then the noise came back but not as loud, when the noise is there it ticks to the rpms, hope you can help?