Just to get a few more views and thoughts:
YouTube Link

This is also in the Tech board but that doesn't get as much notice and I can never seem to find it without a search:

https://www.rx8club.com/series-i-tech-garage-22/more-marbles-can-observations-93836/page6/

I plan on sending this to Mazda for whatever it's worth.

 

That's exactly what's happening with my 8 too. Thanks for posting the video!

 

Gr8Lady are you ready to reach your 1,000'th post!!!!

 

I guess that's the heater core sound...I have a different sound.

 

It's normal. Sounds worse when under load.

Ports opening up around that range too.

It get worse if drive like a grand ma and the carbon builds up.

 

oh my. 15K miles and still no sign of that. that sounds pretty shotty. Crossin my fingers.

 

24+ K and mine doesn't sound like that.

 

clearly air in the heater core

 

And so is it "normal"? Thats what I don't get if its normal then why don't all RX8s produce the same sound. It actual seems much more noticable than it does on the vid.

Even if it is normal I'd still prefer to get rid of it.