Name that noise...with video.
 

Ok folks, this is a '04 MT with 65,000 on the original engine. Just replaced the coils, wires and plugs after I was getting a misfire. Took it to Mazda to get a compression test. My numbers were ok. I have a cheap-o $280 cat from ebay attached to a borla muffler. I am getting a raspy growl from what sounds like the exhaust or cat when my engine is hot and I rev up past 6k RPM. I tried to get the sound in these videos. (It's still kinda hard to hear on video, but much louder in real life.) Let me know if you hear anything amiss.

P.S. This is my first rotary so maybe it's just supposed to sound like that!

Can you post compression test please?

This is what I got from Mazda...
We performed a compression test on your vehicle and found the readings to be "good". These are the readings for rotors 1 and 2;
Rotor 1 kgf/cm2 (1.) 6.7 (2.) 6.7 (3.) 6.6 @ 230rpm's
Rotor 2 kgf/cm2 (1.) 6.5 (2.) 6.4 (3.) 6.5 @ 224rpm's.
Your vehicle passed the compression test with "good" ratings. I do however have some information to share with you regarding a couple of concerns that we noticed. You have a po037 rear 02 sensor code. It shows that the heater circuit has 0 switching ratio.

I'm interested in following this too.. it's the same noise that ManicMazda has, along with several other people.

So far, a lot of people are saying that pre-mixing will solve this issue, and it stems from the fact that the seals are dying now in your car if you have this noise... again this is what people are saying no one has concrete evidence or an explanation yet...

Could you point me to the thread where ManicMazda is talking about that?