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2nd Gen Non-Engine/Transmission Clunk, rattle, and vibration experts: Help!

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Engine/Transmission (1994 - 1998) 98 12V fuel filter

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The details:

98 12V 4x4 quadcab automatic with ~200k miles that I've owned for about 3 months. Its always been a CA truck so no serious rust. I've replaced the track bar, tie-rod ends, front shocks (including shock bolts), steering box, steering shaft, steering stabilizer, and front sway bar links all within the last 1000 miles.

The problem:

My truck has a few different clunks, rattles and vibrations but the one that I'm trying to resolve can best be described as a metal on metal vibration / rattle. It only happens when I'm stopped in gear with the brake on and the wheels straight forward. If I turn the wheel to either side while stopped, the vibration / rattle stops. I believe it stops because the engine smooths out a bit when the wheel is turned and therefore reduces the amount of shaking going on under the hood. The noise is fairly loud and sounds like its coming from directly beneath the driver's floor board. Outside the truck, the noise is amplified by the pickup bed and can be heard underneath the driver's floorboard but is difficult to hear from other locations. The vibration / rattle can be felt, though the noise is significantly more attention grabbing than the feeling.

My exhaust is not contacting anything anywhere and all exhaust clamps / fittings are tight. Nothing in the front end is rubbing or touching. I had a shop check the engine mounts and they said they were fine. My transmission mounts are tight. My pickup bed mounting bolts are tight. My tailgate is not rattling.

Has anyone encountered something like this? I've spent hours underneath the truck prying on things, tightening nuts and bolts, pounding on things, listening for the source, etc. I'm at a complete loss.
 
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Possible belt tensioner bad or if you have a full length cover over the valve covers, maybe the nuts are loose or missing?



Nick
 
It's not the valve cover. The rattle / vibration seems more structural than cosmetic, if that makes any sense.



I don't know how to evaluate the belt tensioner but I can say that the belts are tight and I don't hear the noise at the front of the engine (though it would be hard to hear anything over the noise of engine so I can't say that it's definitely not coming there).



I'll inspect that area more closely.
 
Is there a relatively easy way to inspect the flex plate without removing the transmission / TC? Inspection window? Are there other symptoms of a cracked flex plate other than rattling at idle?
 
JC Buck I have a similar possibly same sound coming from my truck. It is only at a very narrow RPM under load. I changed the flex plate out and it didn't go away.



As far as the flex plate inspection goes, there is a rubber plug on the front of the bell housing facing the radiator. It is on the passenger side a little higher than the top of the oil pan. You can pull the plug and have a buddy turn the motor over with the alternator pully nut while you look through the hole.



I hope you find your rattle. If I find mine I will let you know
 
I've checked the control arm bushings and they're not the problem. I've also replaced the drive shaft center bearing, and although it was destroyed, it was not the problem either.



I haven't been able to check the flex plate yet so I can't rule that out but my gut feeling is that the cause is yet to be discovered. Regardless, flex plate inspection is next on the list- might get to it Sunday. Thanks for the replies. I'll be sure to post the cause if I ever find it.
 
Checked the flex plate bolts today and they were all tight. The search continues... .....



I actually noticed today that the vibration / rattle is there when idling along in gear so long as the steering wheel is not being turned. It can happen while going around a corner or going strait so long as the power steering is not active.



Can the power steering pump make this sort of noise when it is not under load?
 
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