alright, i have a 95 camaro with a 3.4 and i just put in a new engine about 1,100 miles ago. the car n trans has 113,xxx on it and i was just wondering about something. when i start my car in the morning my car will shake a lil more than usual and my exhaust gives like a rumbling/popping sound for a minute or two untill the car is warmed up.. i was wondering if thats because my cats going? i havent noticed this happening till the past few weeks.

 

Mine does the same thing, i asked the same question...

 

If its a poping doesnt sound like the cat, now a rattling durring warm up, that seems to be metalic, most likely the cat.

 

That popping could be a nuber of things:

*ignition coils
*running to lean (usually due to a faulty o2 sensor)
*bad plugs

it's probably going to be one of those. Run your car for a couple of minutes and drive around the block. When you park, look under the car at where the Cat sits. If it's red hot and kinda glowing red then it might be stopped up, but that could also be bad coils dumping too much fuel and the excess runs into the exhause causing the cat to heat up (very hot). So check ones on the list above.

 

Do you notice a decrease in acceleration ESPECIALLY at high RPMS? my car was making the same noise and when i'd get on it at all at high rpms it would feel gutless...come to find out, it WAS the cat, so i had to have it replaced.

 

Mine went out and I just had it replaced along with the muffler and as soon as I drove the car when it was fixed it ran alot better. Because when i revved it would make a rattiling sound and plus the car was losing alot of power. at high rpms it would die out. and feel gutless. also have someone rev the engine for you and listen by the cat you'll hear the rattiling coming directly from it. and not the engine.