About a year and a bit ago, my flex pipe started to rattle... and progressively got worse. It actually vibrated the cat converter to the point of cracking the stuff inside. After it was removed, I could shake the flex pipe and something inside would wobble around.

Anyway... back to the point. I had a new flex pipe custom made (wasnt cheap!), a new cat converter, and also had a manifold bolt replaced (it was broken off) and a new manifold gasket put on.

Since then under accelleration (only seems to be in gear, not when reving in neutral) I can hear a "FSSSSSSSSSSSSSSSSS" (whooshing kind of noise) coming from the flex pipe area. I never got this kind of noise with the original flex pipe (before it started rattling). If i accellerate very slowly I dont get the noise - it mainly gets loud the quicker I accellerate - and especially when the car is under load (like up a hill).

By 'fssssss' noise... imagine that you have some wire mesh, and you blow across it (not through it) very hard... you'll get a 'fssssssh' kind of whooshing noise. Its like that.

Now, i've been told that in the flex pipe (factory) there is a little directional flange/lip thing that directs the exhaust flow some how. Would this be to avoid this 'fssssssh' noise? Maybe the new flex pipe does not have this directional lip thing - as the exhaust place mentioned to me that it sometimes vibrates and they usually just take it out.

OR - could it be the manifold gasket fitted badly... making the noise through the exhaust?

I've taken it back to the exhaust place a couple of times and they assure me that the noise is normal... however I have been in other Magnas and they do not make this noise. I've taken it to a mechanic and they've listened to it up close and said its just the exhaust moving through the system - not much they can do. But, as I said... its not a normal noise.

So anyway, does anyone have any ideas?

Thanks!
Kim