Taken from
here (in case hotlinking of the image doesn't work)
Does your SR20 have a "TAP-A-TAP-A-TAP-A-TAP" noise? The most likely suspect is air in the lifters. If you look at my finger location in the picture, I'm pushing down on the back of the rocker arm on the section that rides above the lifter. While pressing, if you feel any movement, you have air in that specific lifter. SR20 lifters are hydraulic but can not bleed themselves like most hydraulic lifters. To bleed your lifters you must remove your valve cover, the cams, and rocker arms. Pull the lifter out of its sleeve making note not to tilt it sideways, submerse it in oil, and insert a thin piece of rigid metal inside the hole on top of the lifter. Keep in mind, entire lifter must be completely submersed in oil. You will feel a groove with your metal probe, if you press down it will compress the internal mechanism. Do this repeatedly, many times, or until it doesn't depress anymore. Carefully insert it back into the sleeve without tipping it so that air does not enter it. Reinstall the rocker arms, cams, and valve cover and listen to see if the noise persists.
Short answer, if there is air in the lash adjusters you have to take them out to get rid of the air. As long as you don't rev high or push the engine hard everything should be fine. It's not unheard of people leaving the adjusters alone for years and living with the ticking, but I personally wouldn't suggest doing it.