ohhh i had that problem in my rodeo
you need to check the following

one: you have a sufficient supply of oil (prefferably good oil)

and two: that your timing belt is not fudged... because mine was it started sorta ticking then i took it to the shop, it ended up being my timing was off and some other shit, so be careful not to run 'er into the ground..

it sounds like from what your saying tho that the lifters are getting insufficient oil flow to keep them from 'tinking'