(car repair) Intermittent metal rattle coming from under car

[Drazzil]

The rattle changes frequency as I rev the engine at a certain RPM. It happens in every gear. I had the car jacked up and the heat shields checked today when I had my tires rotated. Unfortunately for me my 2006 Toyota Corolla was NOT doing this when I was at the tire shop. I opened the hood and the sound is NOT coming from the engine. It sounds like it is coming from the middle of the car, or maybe the passenger side. I am stumped. I did all the maintenance on the car and everything.

[bdgile]

Catalytic Converter?

[Drazzil]

Possible, but wouldn't that throw a code, and maybe a check engine light?

[Drazzil]

The rattle does not change frequency, but seems to intermittently appear when I hit a certain RPM.

[benedic08]

Got the same thing on my Camry before.. There was something loose from inside the catalytic converter... Didnt really affect the car but was just annoying when accelerating... Changing the cat out fixed it for me... Im not sure if its the same problem but could be it...

[Col. Kurtz]

Check to see if there are any broken exhaust hangers, or any part of the exhaust coming in contact with the underbody. Could also be a worn or broken motor mount allowing the exhaust to make contact. Good luck!

[fissure]

Happened to me on my truck. Same exact thing with no engine code thrown. One of the plates inside the cat converter came loose. I would bet its the cat.

[Drazzil]

Here is a possible wrinkle to the story. About 3 and a half years I was in a low speed front end collision with this car. I had the work done by a reputable shop 5000 dollars worth. Is it possible that a wield popped loose and that is the source of what I am hearing?

[tsolomon]

Had a similar problem with my VW when they replaced the Catalytic Converter and they tightened up the bolts unevenly. The heat sensor on top of the converter at a certain speed/rpm would lift up and hit the heat shield under the car. The dealer couldn't find the problem, but my mechanic buddy got a real laugh out of it when I asked him to look at it.

[shark]

I would seriously doubt that a low speed collision would pop a spot weld loose anywhere.

[mosesbotbol]

Something along the exhaust pipe and/or including the Cat, almost 100% sure on that one.

[DMK]

My bet is the heat shield on the cat.

[Drazzil]

Found the problem. It was the catalytic converter. I was involved in a road accident without knowing it, well I knew about hitting the road debris, and it turns out the cat converter may have had a suicide pact with my transmission, as I heard a buzzing sound like a gnat coming from in my cabin (and no it wasn't a gnat.) I am going to have to take it in again this weekend to see if there is any outside damage to the transmission.