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1991 Sedan Deville
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Discussion Starter #1
I've never had any problems with my truck, but recently a clunking noise is coming from underneath somewhere along the exhaust system. Sometimes it will make a loud noise like something has fallen off, but nothing does. Other times there will just be a little bit of rattle. The engine still sounds strong, so does anyone have any idea as to what this could be? The truck is a 94 Silverado.
 

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1990 350 Brougham (The cruiser), 1988 Mark VII LSC (The DD)
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5,545 Posts
When does the sound happen? If it is when getting on the gas or just letting off 99% of the time is is U joints. It could also be the rear end. How many miles are on it?
 

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1991 Sedan Deville
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Discussion Starter #3
57 000 km, so like 35ish miles? Just randomly, sometimes when accelerating but sometimes when just cruising. When cruising its usually just a slight rattle, but sometimes its a gut wrenching crunching noise. One time I had the crunch when I started the truck, which would kinda make sense because hot air is suddenly rushing through....
 

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1991 Sedan Deville
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Discussion Starter #5
Happens mainly when turning and when on/off gas I've found driving today
 

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1989 Sedan DeVille is now just a fond memory ....
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10,429 Posts
Tie yourself to the undercarriage, have a buddy drive it so you can observe first hand, just be sure to ask him to avoid dips and speed bumps if at all possible.
 

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1990 350 Brougham (The cruiser), 1988 Mark VII LSC (The DD)
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5,545 Posts
Go under there and start yanking on stuff. If something is loose that is probably the problem.
 

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Unicycle
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A damaged cat will cause a rattling sound, had that happen on my '93 Coupe. You can go under it and hit it with a wrench or something and see if you hear anything inside.

Otherwise I'd say a heatsheild somewhere along the line on the exhaust system. Had this happen on the Lincoln, but it would not be a loud clunking sound, instead it sound like pinging under acceleration.
 

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1989 Sedan DeVille is now just a fond memory ....
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10,429 Posts
A damaged cat will cause a rattling sound, had that happen on my '93 Coupe. You can go under it and hit it with a wrench or something and see if you hear anything inside.
Yeah, sometimes they get wrapped around the drive shaft but I don't think you need to hit it with a wrench, I'm sure it's dead by now...... darn cats! :kitty:
 

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1989 Sedan DeVille is now just a fond memory ....
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10,429 Posts
Hey, those guys are all related aren't they? I can see it in their eyes .... :rolleyes:
 

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1991 Sedan Deville
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2,932 Posts
Discussion Starter #12
A damaged cat will cause a rattling sound, had that happen on my '93 Coupe. You can go under it and hit it with a wrench or something and see if you hear anything inside.

Otherwise I'd say a heatsheild somewhere along the line on the exhaust system. Had this happen on the Lincoln, but it would not be a loud clunking sound, instead it sound like pinging under acceleration.
Yeah, its generally a pinging with the odd crunch. The first time it happened it scared the shit out of me lol. I was like "Oh ****! What the hell just happened?" What does the heatshield look like?
 

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1989 Sedan DeVille is now just a fond memory ....
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The heat shield is a piece of sheet metal formed to the shape of the catalytic converter, spot or tack welded to the converter with about a quarter of an inch gap to keep weeds or other loose flammables away from the heat of the converter.

If one or more of the welds have broken, which is common after time with the expansion and contraction, you should be able to tell by tugging at the perimeter until you find the loose weld. If that is the problem a good muffler shop should be able to tack it back on.
 

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1989 Sedan DeVille is now just a fond memory ....
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10,429 Posts
... and you thought I was just all fun and jokes .... :histeric:
 

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1991 Sedan Deville
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2,932 Posts
Discussion Starter #15
Yeah, that is possible. It did sit in a driveway for a few winters before we got it. (From the same relative we got our SDV from, although the deVille was always garaged)
 

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Cadillac CT6 (2019)
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2,292 Posts
A clunking noise when either accellerating or decellerating can be an indication of bad univeral joints; something to consider.
 

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1990 350 Brougham (The cruiser), 1988 Mark VII LSC (The DD)
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5,545 Posts
Look for where the grease may have leaked out. Any black marks on the U joints are probably old grease. Take the two sections of the drive shaft that the U joints connect and twist them. There should be NO movement in them and they should make no noises at all.
 

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Cadillac CT6 (2019)
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You can sometimes hear the clunk by just shifting into gear; that is a pretty good indication of a bad "U" joint.
 
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