If the valvetrain becomes noisy, which is usually accompanied by a rougher noise than the standard tapping noise, hydraulic valve lifters could be to blame. Always make sure that the appropriate level of engine oil is in the engine before inspecting the lifters and after starting the engine wait for a considerable amount of time for the lifters to stop 'clicking'. If it continues, scan the lifters with the engine warm, however, be careful of the engine oil burns. After loosening the valve cover screw, rotate the crankshaft until all the cam lobe which lifts the number one cylinder's lifters are offset upwards; try to push all the cylinder lifters with a wooden or plastic dowel; if one can be compressed only with finger force, it should be replaced. Both the camshafts are five-bearing style, so check the bearing caps for marks and orientation before removing, replace the caps in same sequence and orientation as installed. If the caps themselves do not have a numbering do it with the help of the permanent marker prior to the removal. Turning the engine over a few times by turning the crankshafts can also help to ease of all camshaft bearing cap bolts in a diagonally pattern while tapping on any caps that may be stuck using a soft-faced hammer. Locate the identification marks on the camshafts: if you can't see them, place marks on them; thereafter, lift them out and take off the old seals. Clean all valves and place a number on each of them and pack them in a small bag with the cam contact surface down or use egg trays to pack so that they do not drain. They should then be washed and the valve lifter bores and camshaft bearing surfaces lubricated Before setting the new lifters in place it is important to align them with the identification marks that were made earlier before the component was dismantled. Oil the camshaft journals and the camshaft lobes and then slowly place the camshafts into place. A thin layer of assembly lube must then be put on bearing places of the camshaft bearing caps and the exact places that the bolts were loose in earlier stage, tighten bolts in a criss-cross manner. After apply the valve cover and camshaft sprockets, it is advisable to take off the spark plugs to rotate the crankshaft by hand in an endeavor to ascertain whether the marks on the sprockets coincide with each other after both revolutions. Last but not the least, fit in the timing belt cover then connect the-terminal of the battery and turn on the engine.