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Discussion Starter #1
On start up, I hear a rattling boarder line shaking. Sounds like it's coming from lower passenger side. I looked under hood and had someone else start it. My passenger side cat is shaking violently on start up. It appears to be the source of the noise. Sometimes it doesn't do it at all. Any ideas? Thanks.
 

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cracked manifold im willing to bet. does it sound like a diesel??

apparently the a/c condensor (or some a/c thing) drips on the heated manifold and they have a tendency to crack right above the flange.

OR you may have a rusted out hanger and its not holding its own weight very well, the force upon start up is causing the system to shake

Run seafoam through it to see if your exhaust is leaking anywhere. if its a cracked manifold it will start to smoke up into the engine bay and you can locate the problem that way.... its a place to start the troubleshooting.

also if your check engine light is on get the codes checked out and see if your upstream 02's or downstream 02's are throwing a code
 

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Discussion Starter #3
Just discovered something weird. If I hold my key in they on position for a split second on start up, it reduces the shaking drastically, sometimes eliminating. Could be just a coincidence, only tested it 3 times.
 

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Fuel system? You gave the pump time to build pressure the rattle is probably the engine trying to stay alive while struggling for gas... Could have a bad motor mount as well
 
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