A valve adjustment is where the valves are put back into spec, they have a certain amount of space from the rocker to the valve stem, to accommodate for heat expansion every so often that clearance needs to be readjusted, otherwise the rockers can get too close and start to "tap".
You've never specify what kind of "tunog" like tapping sound also known as "tik tik tik

" or something, cause it is harder for us to give you the right info..... its clueless. Tunog could be anything, get a second or third opinion what could that be.