Exhaust rattling/fumes

[98 SMR AV6]

Hey guys, I'm getting an exhaust rattle around 1500-3000 rpm when my auto trans shift from 1st-3rd gear. It seems to be coming from somewhere between the driver and the passenger side so I'm assuming my high flow cat is going bad.

The question I wanna know is that, if the cat goes bad does it create a bad exhaust fume or do I need to change the o2 senors? Every time I drive with the windows down, I can smell the horrible exhaust. This never happened before until the rattling started to happen.

All help and responses are greatly appreciated!


EDIT: It doesn't rattle when I'm in park and It doesn't rattle when I give it a rev, It only happens when I drive.
I had my friend drive next to me and he heard it somewhere under my car.

 

[fastflyinaccord]

My first piece of advice is to look under the car while it is running and see if you can tell where the rattle is coming from. Either that or have someone look under while you rev the engine with the car in park.

Either the cat is going bad (I had one go bad and their was no smell) or you scraped somewhere and have a hole...maybe a bad gasket??? just some suggestions

 

[98 SMR AV6]

My first piece of advice is to look under the car while it is running and see if you can tell where the rattle is coming from. Either that or have someone look under while you rev the engine with the car in park.

Either the cat is going bad (I had one go bad and their was no smell) or you scraped somewhere and have a hole...maybe a bad gasket??? just some suggestions

oops I forgot to put that nothing rattles when I'm in park and when I rev it up to 5k rpm I don't hear anything either, it only happens when I'm driving. I jacked the car up last week, took a look at it and nothing seems to be loose. So idk whats going on..

 

[fastflyinaccord]

A rattle and nothing seemingly loose would indicate to me that maybe some of the honeycomb material inside the cat has broken loose...I had this happen as well and it seem like most of the noise was caused at low rpms

 

[98 SMR AV6]

A rattle and nothing seemingly loose would indicate to me that maybe some of the honeycomb material inside the cat has broken loose...I had this happen as well and it seem like most of the noise was caused at low rpms

That's what I was thinking too..I'm going take my cat off soon and see what seems to be broken loose inside. Thanks for your suggestions and help, I'm assuming the honeycomb that broke inside was your cat?

 

[fastflyinaccord]

That's what I was thinking too..I'm going take my cat off soon and see what seems to be broken loose inside. Thanks for your suggestions and help, I'm assuming the honeycomb that broke inside was your cat?

Yes, inside the Cat is a honeycomb material that filters out the really harmful stuff. Sometimes a hit, scrape, or just constant bumping can lead to the material breaking loose. A lot of times it will just rattle around inside the Cat itself or it can actually be pushed out and get stuck in the exhaust pipe


Rep is always appreciated

 

[001Stunna]

OP, jack up the car and using a rubber mallet hit the catalytic converter and see if you hear anything from inside. Don't hit it to the point where you dent it.

In addition if you can, get the car on a hoist while its running in idle; in the mean time check for leaks around the flexpipe and other gaskets using your hand(you'll feel exhaust gas blowing in your hand). To make it easier you can have a buddy cover the tailpipe to create more pressure in the exhaust and make it easier to pin point the leak. Do this in intervals and do not just block the exhaust for a long time.

 

[98 SMR AV6]

OP, jack up the car and using a rubber mallet hit the catalytic converter and see if you hear anything from inside. Don't hit it to the point where you dent it.

In addition if you can, get the car on a hoist while its running in idle; in the mean time check for leaks around the flexpipe and other gaskets using your hand(you'll feel exhaust gas blowing in your hand). To make it easier you can have a buddy cover the tailpipe to create more pressure in the exhaust and make it easier to pin point the leak. Do this in intervals and do not just block the exhaust for a long time.

I'm jacking up my car again tomorrow to take a look at it, I'll be sure to do that thanks!

Do you or anyone know why my exhaust is giving off bad fumes?

 

[001Stunna]

I'm jacking up my car again tomorrow to take a look at it, I'll be sure to do that thanks!

Do you or anyone know why my exhaust is giving off bad fumes?

Exhaust leak at either the flex pipe, one of the joints(gaskets) or a hole possibly...

 

[98 SMR AV6]

Exhaust leak at either the flex pipe, one of the joints(gaskets) or a hole possibly...

All I know is that i scraped my flex pipe and its leaking a bit so maybe thats the problem? If so is there something I can wrap in the meanwhile before I get it cut and welded?