@CATS
It actually didn't sound much worse than the normal tic-tic... I actually opened the tappet cover to take the hydraulic lash adjusters out since the rev. to 3.000 rpm for 15sec procedure didn't change anything. I didn't expect to find this!
@7pajeros
I bought the vehicle with no history so it's actually difficult to have a good idea of the reasons that lead to this.
But I agree with you on the cause, too much play that allowed the rocker to shift. It was still located at both its end on the lash adjuster and the valve. Luckily I guess otherwise it would have been a whole different story if it had come completely loose
Lash adjusters were supposedly "serviced" when I had the head done almost two years ago, but everything that was done back then seems to have needed re-addressing... Shoddy workmanship? I'd say yes 100%...
I've let the adjusters soak in clean oil and have bled them, and they don't appear sticky. But maybe I'll be safe and replace them.
FYI the ticking noise was coming and going, that's was I wasn't too alarmed about it.
Oil and filter changed every 10.000km with Castrol GTX and the last one with Delo 400.
Thanks for the comments.