I have a intermittent rattle coming from what seems to be my muffler. The car has newer flow master mufflers and 2 straight pipes with no cats. This was done when I bought the car. The tailpipes were rusted because they were original so they cracked off from the mufflers. I brought it to an exhaust shop to get it fixed and when I got home I noticed a slight rattle and thought nothing of it and continued to use it for the next couple weeks and the rattle occurs out of nowhere and sounds like a marble rolling around in my muffler. Do you think this should be their bill at the shop or could something be rusted inside my newer mufflers?

 

Something could def be coming apart in the mufflers. If you can, get under the car and start shaking/knocking the exhaust around and see if you can locate the noise.

 

The thing is I have been checking it randomly the las few days and every time it is a different noise sometimes it will rattle when I close the door and other times it wont rattle for a whole drive. I would take my muffler off to see if I could knock something out but everything is welded solid so this poses a problem.