I have a 2006 Screw Lariat with the 5.4L FFV engine. I've noticed a slight vibration or rattle noise which seems to be coming from the rear driver side of the engine compartment when I am in drive and stopped at a light. Then when I start off from stop the rattle gets louder for a second then goes away until I stop again. Sometimes it's very loud other times you can barely hear it. I've also noticed a strong vibration in the gas pedal and steering wheel when I hit 72 MPH. I've taken it to the dealer twice now and they have told me they didn't hear anything the first time (without driving it) then the second time they said it was caused by the AC system and if I turned it off I wouldn't hear the noise because the noise was the system's vacuume or something (living in North Carolina driving without AC is not an option, espically in a $40K truck). Without the AC on the noise is still there but is not as loud. I had a 2005 Scab that I traded for the Screw when they had the 0% deal and never heard any of those sounds in the other truck with the same engine (5.4L but not flex fuel). I've also noticed when I was checking under the hood that when the truck is parked running the brake fluid container vibrates so much it causes the brake fluid to jump around like someone was shaking the container. The vibration noise is not there in park. Has anyone else had these problems and what should I be telling the dealer next time I take it in? I love the truck and the extra room over the Scab but these noises are driving me crazy. Thanks.

 

No one has any ideas what might be causing this? I was going to take it into the dealer next week. If it helps it only starts to do it after I drive for a while. When I first start off there's no noises, then after I drive about a mile it starts off slow then gets louder the longer I drive. My RPM is around 650 at idle which most of the time seems good, except today I noticed while I was parked it was running a little ruff. Even if the dealer is right and it has something to do with the AC I still can't believe it's "normal" to have that noise. Thanks again to everyone that's read this post.

 

Well as far as the vibration, you have to try and "reproduce" the conditions as best you can while looking at the engine and listening. I can't assume that the brake fluid jumping around is any good. I'd try to isolate that problem first. In my 2000 I had a rattle from the cover on my fuse box. Took me about 5 minutes to narrow it down. As for the vibration at 70+, is it a whole truck vibration...or does it feel engine related like it is surging or misfiring?

 

the vibration at 72 is mostly in the gas pedel and steering wheel. it doesn't seem to effect the rest of the truck. As far as isolating the other sounds, I've tried that but when I start it up and throw it in drive I don't hear it. It's not until I drive for a while I hear it while stopped at a light. then starting off from the light the vibration get louder for a second then stops till I stop at another light. I'll try to take it for a drive this weekend and come back and see if it makes the sound when I get back home. Thanks for the response.

 

I have the same rattle. I have found it's worse on a slight incline and right when I start accelerating. It is only about 1 second long, but if I hold the accelerator at the point where I hear it, it will continue for a while. I had my fiancé drive while I was inside/outside, with the hood open/closed, door open/closed, and it is definitely coming from the under the dash. A/C doesn't really affect it. If you find out what it is, let me know! I'll keep looking too.

 

WOW, That's really something - It's so bad it shakes the brake fluid reservoir. Never heard of it...BUT, There is a TSB - A "Customer Concern" TSB from Ford Motor that has to do with the "Cat Shields" @ idle and just above. You fix this issue w/band clamps.. -



As far as the high speed vibration - I would guess that to be driveline oriented. somethings getting hot at high speeds , like a bearing, driveshaft, differential fluid, wheel balance out...etc...

 

Open the hood and look at the air filter snorkel where it connects to driver side fender. Mine came loose and caused the same symptom. I pushed it back in and the noise was gone. I hope it's this easy for you.

 

regarding jbrews reply too, I had the serial number tags rot off the actual cats and lay on the heat shields causing a terrible sound! Just removed it with a long screwdriver, and silence is golden!

 

Do you have the stock exhaust manifolds still or aftmarket headers I installed headers and the egr tube from the headers to the manifold would rub against the steering shaft and vibrate during the first few seconds of excelerating then go away.You could actually feel it in the steering wheel it was a loud rattle...check it out.

 

Mine did that - exactly like the OP described the noise above. So did a buddy's 99. It was more of a irritating chirping sound - It was worse in drive, brakes applied with the vehicle stationary.

Wrapped the band clamps around the "larger" cats that are right underneath the floor board . No more noise. A couple years later , the front cat heat shields started making noises.

I just offed all the cats at that point and installed LT's & a couple HF Cats. The exhaust makes a nice noise now

 

Yah brewster, I'm hopin mine last a good long while, but when they go......hi flows! :-D

 

I have the same noise on a 2005 king ranch onlt when I sit at a light in drive or braking will cause it too. Put it in nutural and it goes away or foot off the break and back on.I see that the air hose is not in the fender snug.I will start there.The cat band could be it as well.Any other ideas if not those two?