I have used motorcraft filters and the 5w20 oil at every 3,500-4000 miles. I have noticed on several occasions a quick metallic noise for about 1/2-1sec upon cold start up. However it might only occur 3-4 mornings out of the week. I changed the oil/filter and still get it about 50% of the cold start ups. Its a '06 w/116,000 miles.

Could the check valves still be bleeding through?

Any oil additive that I could add?

 

possibly cam phasers starting to act up ...imo