When surfacing some 2x6 redwood planks, the Dewalt planer makes a clunking
nose with the cutting head hesitated and jumped up a little in a cyclical
fashion about every couple of seconds. This results in lines across the
grain about every 4 inches apart that corresponded to the clunking sound.

I've checked the cutting head and it runs smooth without load. I also
removed the blades and tested the rollers under load and it runs smooth as
well. The external roller chain drive seems to be ok too. The blade lock for
changing blades is not jammed with the cutting head rotated freely by hand.
Belt for cutting head looks ok too. Motor brushes are in good condition.
Replaced old blades with new, same problem.

I'm running out of things to check other taking the cutting head apart.
Broken gear in the cutting head? Anyone has a similar problem? Any ideas?

Thanks in advance.