I did a search but didn't see any posts that appeared similar to my issue.

All out of nowhere, I have a high pitched buzzing/rattle sound coming from under the car near the tranny area, on the passenger side. It seems to manifest itself once the car warms up. Its a very "Tiny" sound, like a heatshield, but I've had the car on a lift and can't see to find it.

Yesterday I could hear it while the car was just idling, although usually I hear it accelerating in the 3-4K rpm area.

I can't think of anything wierd that has happened to cause it. I don't think its the cat, we checked the heat shield. Can the high flow cats cause a vibration like that after a while? The fact I could hear it at idle makes me think something is making contact with something else, I just can't pin it down.

Ideas would be appreciated.

 

I've recently noticed a similar thing. I've got the RP Supercat. Let me know if you figure it out.