Rattling at idle

[5point0dude]

Hey guys, I have a question that I cannot find the answer to. I have a '91 5.0 LX and when I start the car it starts up fine, but a second or two after startup I'll hear this loud rolling/rattling/clanking sound for a second then it goes away and the car is fine. As I'm driving, I hear nothing out of the ordinary, but when I'm at a stoplight idling for a little bit, I start to hear the same noise from startup, only now it keeps going and going the whole time I'm idling, and the second I touch the gas to go, the noise stops. I'm not sure but it sounds like it's coming from under the car, like the transmission or driveshaft, and I do have a 5-speed. To me, that's where it sounds like it's coming from, sometimes I can feel the vibration from the rolling/rattling/clanking under the floorboard. Also, whatever it is, it sounds like it's spinning or rolling, and it sounds kind of heavy too. Any info would help because I have no clue where to start diagnosing. Thanks.

 

[fivespeedsteed]

heatshield rattling? usually it does it all the time at idle. this is for the catalytic converter btw.

 

[MahFiVeOh]

I had something very similar happen last year.One of my cats went bad and started to rattle.It almost sounded like an engine knock.Jack up your car and see if it rattles when you tap it with your hand or rubber mallet.

 

[5point0dude]

Thanks guys, I completely forgot about the cats, I remember reading about someone else having this problem, I'm pretty sure that's the problem now. If it's the heat shield or cat itself, what's your suggestion on fixing it? Thanks.

 

[MAC'n89Blckstng]

Get an off road x pipe and your car will be louder and a lil faster.

 

[85_SS_302_Coupe]

Thanks guys, I completely forgot about the cats, I remember reading about someone else having this problem, I'm pretty sure that's the problem now. If it's the heat shield or cat itself, what's your suggestion on fixing it? Thanks.

Either tack weld the shield so it doesn't vibrate, or take it off completely.

 

[5point0dude]

Thanks everyone. I was planning to get a catalytic x-pipe in the future to gain the extra ponies, sound better, and pass smog at the same time, but now I have a good excuse to go get one now.

 

[Cobra912]

had the same problem on my old notch. cat heat sheild rattled like crazy

 

[Stableboy]

I have the same problem. I know the shield is there for a reason, but anyone heard of issues if you remove it?