Unknown Rattle
 

I have a 2010 F150 lariat 4x4 3v
I am getting an engine rattle at idle... The rattle only occurs when I reverse up a up a hill slowly. It can be trigger by reversing hard. Also one time it was trigger by a sharp turn at idle.

I have replaced the Cam phasers, installed a high pressure oil pump, ratcheting iron tensioner, timing chains, and chain guides along with related gaskets.

Despite replacing all that I still get the rattle. Any thoughts?

More details
 

The rattle continues in and out of gears.
The rattle is only trigger by slow idle speeds under a load
Once the rattle begins it stays until I Rev the engine up then it goes away and doesn't return until triggered again.
Water pump rattle trigger by slow belt speed maybe?

What phasers were used? OEM Ford? And could the rattle be the hubs trying to engage rather than the engine? Based on when it rattles, perhaps the vacuum is too low or is leaking just enough to cause issues when the rpms are low. Hence, higher rpms under no load will give you a stronger vacuum.

Did you drop the oil pan and clean the pickup tube? I had this happen once in my 2009 after a long highway run and using very thin 0w20 oil (toyota 0w20 which is on the thin end of the 20 weight spectrum when hot). Stopped and backed up and it rattled and ran rough. I started using 0w40 weight oil (castrol, in my case) and never had it happen again for years after that. I would suggest that the bearing clearances in your engine are flowing more oil than new and the pressure on the pins in the phasers aren't locking allowing them to rattle. your 3V 5.4 engine was spec'd for Xw30 or Xw40 weight when it first came out in Australia years before it arrived in North America. I would try a grade heavier oil. It worked for me.

VCT solenoids were faulty. Updated oems where put in and the problem was fixed.