I posted this on the mailing list, but trying to cover all bases.

I've just noticed in the past day that when the truck hits 34mph, I hear a loud hum. Sounds like a high frequency rattle, but definitely metal. It's an 97 ORP, automatic, 4.6 V8. I just had the tranny fluid flushed, the transfer case and diffs serviced. This doesn't appear to be a shift point at 34mph as the tach does not change or anything felt. It's also definitely emanating from the front passenger side. Rattle only exists at 34mph, no more no less and doesn't seem to be linked to any particular rpm on the tach. And this was happening before the tranny service. Any ideas?

Scot




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97 F150 ORP
Towing/trailer package, 3.55LS
34" Mickey Thompson Baja Belteds, Requisite K&N Airfilter
JVC Kamelon CD Player, CB, bug shield, window shields, and other goodies

 

My thoughts:
1. Exhast system?
2. A loose heat shield?
just a couple of things to look at.

Hobbit

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99 XLT,4.6L Auto,4X4,tow pkge,Factory Side Steps and Mudflaps, K&N filter,BugflectorII, Amazon Green/Silver, Pace Edwards Rolltop Cover, still want a Superchip and by golly I'm gonna get one (just as soon and I hit the lottery )

 

I think hobbit is on the mark. This sounds to me like the heat shield above the muffler vibrating.

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1999 F-150 XLT Supercab Black factory stepbars Flareside Sport Package Oxford White Full tint - all windows. Bug Shield CD player 17" wheels, K&N Air Filter, Ford Soft Tonneau Cover, Gibson Super Truck, "Did it myself" Undercoating, Herculiner, Image Tailight Covers, SUPERCHIP

Stereo Mods:
Clarion Pro Audio SRC5752s mounted in the front, tweeters mounted above arm rests.
Kenwood KFC-577Cs mounted in the rear doors.
B-Quiet sound dampening installed in all doors, three layers on rear wall, and entire floor board done as well.

"Freak on a Leash"

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Thanks, I'll look into that part. Just to play devil's advocate, why would it vibrate only at 34mph and no other speed? It's not related to the rpms either. Would the speedometer be capable of making these noises?

Scot

 

sounds like a harmonic vibration to me, the vibration acts like a sound wave and when its hits a particular frequency the metal in the area (heat sheilds,exhaust tubing etc)get a kind of resonating hum and/or vibration. Especially if the component is slightly loose. We have all heard that some of our trucks have had vibration issues in the exhaust systems before. I would look into that first.

Hobbit
Using common sense and "deep thoughts" to help diagnose problems.


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99 XLT,4.6L Auto,4X4,tow pkge,Factory Side Steps and Mudflaps, K&N filter,BugflectorII, Amazon Green/Silver, Pace Edwards Rolltop Cover, still want a Superchip and by golly I'm gonna get one (just as soon and I hit the lottery )

 

I have the same vibration in my 2001 supercrew. It is coming from the passenger side.
I ripped the door panel off thinking it was some metal linkage or window tracks vibrating.
I now think it is coming from the exhaust system. I can shake the tailpipe and hear a metallic vibration from inside the muffler. I have an appointment for the dealer tomorrow morning... hopefully they will figure it out.
Its driving me crazy`

 

Do all of you guys have a manual shifter for the 4X4?

 

Yeah, mine's a manual shifter. I was under the truck this past weekend changing the oil when I noticed something strange. Up under the front by the transfer case (I think) there was a compenent inline that (bear with me here and my technical jargon) looks like a small tappered coffee can that has a hard plastic lid that snaps on it. The lid was hanging off and I snapped it back on and the vibration seemed to disappear. It's back this morning and I'm willing to bet that the lid of this "thing" fell off again. I couldn't find any reference to it in my manual of Haynes book. Anyone have a clue as to what this component is from my neanderthal description? I could make a cave drawing. lol

Scot


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97 F150 ORP
Towing/trailer package, 3.55LS
34" Mickey Thompson Baja Belteds, Requisite K&N Airfilter
JVC Kamelon CD Player, CB, bug shield, window shields, and other goodies

 

now you've gone and got me wondering. i crawled up under mine and took a look around, but I didn't see anything that seemed to fit your description, so what is this component in line with? is it near the transfer case, or the front axle? now that you've started talking about it, I can't rest until I find it.

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BigBunnell

98 F150 4X4 XLT flareside V6 5sp K&N Flowmaster and some other goodies

 

Thankfully, I took a couple pictures of it with the digital camera. I'll try to post them here tonight to let you look at it.

Scot

 

Joegood:

I have the same thing. I can just barely hear it. I just ignore it. When I bought my Cobra used, I had a similar sound from the rear left. After changing the gears, removing the axels and brake components, the noise was gone. I think it was the brakes, although nothing was changed, just removed and reinstalled.