New one for me...raspy exhaust?

[Dragonwind]

I've recently put back my Maxspeed headers and just added the 200cel cats. I briefly had the Maxspeed muffler back on but went back to the stock muffler. All was well till I put the top down.

When cold or even 10 minutes after shutting off then going again, there is what sounds like a rattle or rasp when under load. I've poked, prodded, and banged all over the entire exhaust line and cannot reproduce the noise, plus it is dead quiet inside the car (meaning I can only hear this externally). Typically any rattle (which I have had before) will be audible in the cabin. After the exhaust gets to full temp the rasp is almost gone.

Now who knows how long this has been doing this but I am wondering, is this from a bad muffler baffle or the high flow cats? I've given up on finding any external problem.

I didn't hear this when I had the Maxspeed muffler on. Before I sell it maybe I should put it back on and see.

Anyone else ever encounter something like this? Any things are appreciated.

Thanks
Chris