Anyone familiar with this noise?

[flashstang04]

Hey guys,
I am having a "buzzing" noise come from my passenger side whenever I get to about 1800 rpms, now I know this has to be a vibration, but I dont know what can be causing it because I cant tell that anything is loose down there, it will stap after about a second, but it is loud next a curb or wall, any input would be appreciated!!
-Daniel

 

[nickthegenius]

Its probably just some sort of resonance. It could be anything from a loose muffler hanger to something rubbing in the exhaust system under the car. It could also be a shield on one of your cats buzzing. I would just jack the car up and see if you see anything funky with the exhaust system.