Finished installing back catcon liao. what a long day
Long story short, the sound is gone liao.
Frank, Tommy and gang have identified that the sound is vibration from the muffler box.
Because using straight pipe, air flow hits the muffler box fast and hard, and our stock muffler box cannot handle it.
One solution was to use a bullet, to slow the air flow, but Tommy(he's the resident expert @ SC) said there would still be noise.
one option was to do this:

Once swapped with their muffler box, I quote Tommy, the "pu$$y" sound no more, and instead got "sexy" sound.
Honestly, it really did sound awesome. Even the IS250 owner who was there complimented the roar, said sounded like his Lexus, lol (I told him sound same only la)
In the end, I still had to keep noise down, so they put back the catcon & original muffler box, and ta-da, no more sound.
Everything done today was FOC.
BUT, there was definitely less power liao. Slightly less, but definitely can feel. Again, last night and this morning driving with 421+decat was really an experience.
Finally, I'd like to recommend Super Circuit to anyone who wants to mod exhaust.
Not only were they knowledgeable in their field, the after sales service was really 150%.
Remove catcon, install extractor, 'free' dyno, test muffler box, take out muffler box, reinstall catcon, serve coffee, share stories etc. It was clear Frank was determined to make sure the RM1170 I spent yesterday was worth every sen.
Frank also mentioned he is more than happy to help out LYNspira members. Just drop by anytime and who knows, GB can get value

fuyohhhh... konpem goin for supercircuit jor...
as long can use mijubiji mapping ok mar...