After several weeks of searching on forums, google and testing ideas, I still cant find the source of this noise. (Video attached, play it in hi volume)
My first thought was that the bubbling noise was cause from a leaking exhaust.
I have J's racing header, berk 63.5 test pipe and Tanabe medallion exhaust.
I read that some people were having leaks with the connection of the berk test pipe and header so first I reinstalled the original cat , the raspy noise went away, but the the bubbling noise was still there.
I thought that the problem still could be the attachment from the J's Header to the cat or test pipe so I follow another thread recommendation of closing the gap with small gasket between the main gasket and the cat. (Noise still there)

https://www.s2ki.com/forums/s2000-un...1133599/page5/

The noise comes around 4k to 6k and it sound like a fine rattling or air bubbling. I looked all the other exhaust connections, but they are ok.
My next thing to try is to look inside the area where the shifter is located or switch back to the original exhaust.

Any ideas/ help will be much appreciated.

Thanks.