Ok, so Ford basically blew me off on this one and its befuddled many.

I have an 08 Crew cab, extended bed FX4

at 105K it rattles at very low speeds to stopped. Problem goes away once I give it a good pedal full of gas. Happens almost 95% of the time in reverse.

I brought it to local Ford dealership and after a lengthy conference they believed that the motor would have to be pulled to find the issues and there was no guarantee it could be fixed, resulting in then needing a new motor. (note: began at 105k. warranty expired. lucky me)

1st local mechanic (also stumped) said run a thicker oil. I have been running 20/50 and its really helped but problem still exists. (rattle is EXTREMELY bad following oil changes)

2nd local mechanic finally was able to witness rattling and got underneath with a stethoscope and thinks it could be a timing chain issuebut really doesn't know. The scan says cam issue.

Ford dealership says this is a rare problem and they only get 1 or 2 a year with this issue. Said it could be a small piece of plastic in the motor.

So nobody has any idea whats going on unfortunately. I'm glad I found this site. Getting all kinds of info about my truck.

I LOVE this truck and am hoping to solve this issue. However Its a long way to go and very expensive if we can't diagnose the problem and may force me to trade it in.

Thanks