Mr. Neptune

Any update on what the dealer found? Mine has it too and when I put my Edge programmer in "extreme" mode the noise is even more pronounced.

TomR

Have you tried a higher octane gas?

Mr. Neptune

Yup....even tried octane boost with 91oct with no change in condition. I still have the rattle while in stock mode but just a little and when in a programed mode the rattle is louder.......

Mr. Neptune

Bump...

apoirier594

I have a 2wd 99 4.6, and mine also has a little rattle under light acceleration, usually up small hills. If I punch the gas or get up to speed it stops.

Any conclusions?

HoppyFX4

I got out in the driveway yesterday and did a little fine tuning. With my issue, the problem was a "rattle" under light acceleration between 1st and 2nd gear. Very seldom would I hear it from 2nd to 3rd, and if I did it’s always under 2500 RPMs. I first noticed it in April AFTER I took out the intake tube and housing to clean the TB and MAF. So I took it all out again, re-cleaned, and re-installed. Double checking each bolt...no success. I noticed that when I hear it, it's on the passenger side and I CAN feel it on the pedal. I'm stumped...if I can feel it on the pedal then it must be related to either air intake or exhaust, correct? I doubt it's a heat shield. Then I saw where someone mentioned better fuel...I’ve been cutting corners and putting in Kroger cheap-o fuel. So I’m going to try these next 2 steps...

Step 1: Fill up next with BP, Shell, or Chevron
Step 1a: Dump a can of Seafoam or Gumout with it

Step2: Check my cat-converter, in March I threw a code and the dealer replaced my left side (passenger side) cat. This is a hunch, but maybe it's loose?

I'm still curious about the 4WD actuator though, my FX4 hasn't had any issues engaging 4H or 4L. I've used it pretty well a few times with success. Doesn't mean there is an issue though.

Other than that she's a mean 07 FX4 with 101K that hopefully has another 100K to go

HoppyFX4

*UPDATE*

I found my issue! It was a heat shield/skid plate...on my passenger cat. When I got the truck in Jan, I threw a code in Mar before my 3 month warranty ran out. Dealer replaced, but not a Ford dealer. This cat doesn't look OEM, but pretty darn close other than the crappy heat shield/skid plate. It's barely held on by 4 bolts, it was loose on two and completely disconnected from the other. I was able to take it off by hand very easily. So far no rattle at all under acceleration. What are the ramifications from not having the shield on there? I'm sure I can reattach it with some JB Weld...

If no one replies, I'll just post the question in a new thread. So don't feel obligated, thanks for those who suggested the ideas. I'll probably still run a can a sea foam and a tank of high octane for kicks and giggles.

Racerx535

Can you post some pics of it's location? I have narrowed it down to the rear and I believe I am having the same issue as you. Thanks

HoppyFX4

The cat is directly under the passenger seat, so it's not in the rear. I'll post some pics when I get home from the office though.

'08f150stx

The first and the cheapest place to look. I also read a thread somewhere a small plate was welded somewhere above the location where the heat shield is.
Good luck, hope that is where yours is too.