2003 Honda Civic Noisy valves on cold start

My Civic Hybrid's valves are noisy on cold start (about 30 degrees F and below) for several minutes. I had the valves adjusted by the dealer to get ready for the winter. Now, the valves are noisy at 60 degrees F for about 1 minute on cold start. I went back for a readjustment, and the dealer pulled the valve cover and showed me that the adjustments are correct (the engine did have several hours of cool-down time before the check).
I am wondering about sludge causing slow oil movement to the top of the engine, even though I've faithfully changed oil every 5000 miles or so. But would 0W-20 really move that slowly?
Could this lead to engine damage if I don't get to the bottom of this?
If all is correctly adjusted, why didn't the engine do this when new?
What causes the noise to recede in a few minutes?
This is really confusing me - thanks for any thoughts