Noisy @ High Revs

[DATOOR]

Every time I let my right foot get carried away, the engine sounds as thought the teppetts/lifters are loos or going to fly through the hood.

I change the oil every 10k km and have used Lucas additives.
This sorts the problems out for a day or so, then starts.

as winter is approaching and I pull heavy loads and max out on the engine, I need to solve this asap.

Any ideas??