Bad exhaust sound but no bad exhaust!

[xexman44]

2007 Yaris, for no reason that I can tell, you hear a sound like the exhaust just ripped open. Your sure there is a hole or a seem that came apart but there is nothing wrong with the whole exhaust system. When you start the car it runs and sounds perfect. Then all of a sudden you hear the noise. I thought it would be an EGR problem but no EGR system on the car.
Even when the noise is happening and your standing there looking over the engine, you can't find anything wrong. Been a mechanic for a long time, no genius but this has be baffled. Any thoughts or ideas? 62,000 miles on the car. Runs perfect otherwise. Even runs good while it is making the noise. Like taking a kid to a doctor, when you try to work on it, it works perfectly.
Appreciate any thoughts. Thanks guys.
Joe B

[CTScott]

Check the metal donut gasket between the header and the exhaust. A few people have had them disintegrate.

[spoutnick]

Check the metal donut gasket between the header and the exhaust. A few people have had them disintegrate.

That was my prob!

[TLyttle]

Not sure if it would work on these new computer-controlled cars, but in the old days we just stuffed a rag into the exhaust pipe and listened for the leak. Works better with 2 guys, one to plug the exhaust, the other checking around the front...

[Astroman]

That was my prob!

I swear this site needs a kudos option :laugh:

[CoryM]

Check the metal donut gasket between the header and the exhaust. A few people have had them disintegrate.

This ^
If the car is auto try rocking it forward and back while in Park. This rotated the engine and flexes that joint.

Other likely thing would be broken baffle in the muffler, but you would hear that out the tailpipe.

[xexman44]

Thanks for the ideas. That is one thing I have not done yet is stuff a rag in the tailpipe, need another person to help me with that one. The most confusing part is that it still does not do it all of the time. Sometimes it is just as quiet as brand new. But when it is making the sound, you can't find out where it is coming from. I'll keep looking, I guess when whatever it is burns all the way through I'll find out what was wrong! Is that a good technique or what?