They hydraulically fill with engine oil. It takes a lot of effort to get them to push the oil out. Usually a vise. But it may also damage the adjuster. The only step in the workshop manual for checking them is this "Inspect the hydraulic lash adjuster and roller follower for damage. If any damage is found, inspect the camshaft lobes and valves for damage" If the noise is the same as before replacing the adjusters I suspect you may have an issue else where.