I have a 97 accord with a cat back flowmaster setup. I recently replaced a busted motor mount in the front and now when i am slowing down i get a harmonic vibration coming from the cat and midpipe area around 1750 rpm. it only occurs at 1750 rpm give or take. It does not matter if the pipes are hot or cold b/c i know when pipes are cold they seem to sound tin cannish.

I have bent the heat shield off the pipes and hangers so there is no contact between the two. The cats heat shield is rusted but there is no sign of rattling.

Does anyone have any idea about this?
Is it woren out gaskets between the cat and midpipe or could it be something in the manifold. Any suggestions are helpful.

Thank you

 

This is the first thing that comes to mind;

 

if this was the problem wouldn't I have an exhaust leak though from woren out gaskets?

 

no they don't leak they just buzz

 

is there any indicator on the gasket to tell that it is bad? Or is it just a replace it and the buzz goes away