Engine noise

[cart]

When the engine is started for its first time for the day I get this loud
SOLID tapping noise,the noise is not constant, on start up it taps for maybe
5 secs,goes then comes back and goes i find usually taking the revs up to about 1100 rpm then to idle and back up again increases the noise level and speed due to the higher revs,then it will go and starting the car anytime after that there is no noise.
However there are times when i start the car first up in the morn and there is no noise at all???
I have noticed that at about 1100 to 1300 rpm in park i can hear what sounds like lifter noise,this is audible whether the start up noise is there or not, this is also noticable when i throttle off when driving at about 60klm p/h again in the range i get it at idle but with the car moving.
The engine is serviced regularly using Castrol Magnatec 10w/40 and has done 135000 klms, its a 4 ltr 6 cyl series 1
The start up noise has only been there since i had gas fiited i am pondering if there was a backfire when they where tuning it? Or it might be coincidence?
srry about long post.Any suggestions Thank you....