Ok. this just started up.. not sure where the sound is coming from.. Put the car up and shook everything and its all tight.. no wobbles..

Turn the car on.. nothing.. about 30 seconds later a rattle starts.

most noticeable when the car is idleing. I am sure its there at highway speeds but its drowned out by other sounds I am thinking..

sound changes as engine RPMs increase it increases.. Cluth in or out makes no difference. Rolling makes no difference..

any ideas of where to start looking!??! Almost hitting 90K miles. I have NOT done the following:
any mods (the exhaust is stock..)
changed plugs
replaced the serpintine belt
replaced any pulleys

so could this be some sign that I need to do some maintenance or could it be the tranny? I just had the clutch replaced 4K miles ago.

 

Catalytic converter rattle? It can be pretty loud.

 

.. YEp. They'd mostly rattle at idle..

 

so, ya think its finally gone south? hmmm lets hope! hehe
I think I still have that recall paper..

 

If it's coming apart inside try beating on it with a rubber mallet with the engine off - don't leave any marks though, they may not honor the warranty. Also make sure the 02's are in tight, friend of mine had one of his rattle - believe it was the metal ring between the sensor and the cat.

Edit: Should be throwing a code if it's the cat, right?

 

Not necessarily. Mine would periodically throw the codes for Catalyst Efficiency Below Threshold (P0420/0430 ... think I was getting 0420) but when one of mine actually failed (sounded like a can of marbles being shaken around under there! ) there was no code being set .

Likely, that's the problem.

 

Sounds like a cat to me, exact same sounds, try the mallet idea, you should be able to even bash it with your fist hard enough to make it rattle.