Engine is ticking and CEL is on code 1406

i have cleaned the throlette body, egr valve and all around it and reset the light. light never comes back except in the morning, when i start my engine. If I will reset it again it will not show up untill the next morning.

engine is ticking. I wouldn't say very loud, but in the morning is louder and you can hear the metallic knock for about 5 sec, than engine light comes up showing 1406 code..

any ideas?