The other day and today I heard this vibrating noise from the exhaust/pipe of my sedan when I started cold. Seems like something is loose on the back where the exhaust is or maybe the eschaust is hitting when it is vibrating cold. I heard it when the car was cold in the morning as I happen to go back to get something from the trunk as my car was warming up. It seems to go away after that.
Any ideas or anyone with same problem? solutions??

Thanks

 

It is probably the valve inside the muffler.

 

yes, the stock exhaust tip is making the rattle. Next time when you hear the rattle again, you should go down and check if its the tip that is making the noise. Becareful with it, if you try to fix it or lose it...the rusted bolt might just break like mine did, then i change to stillen T-D