Strange buzz/rattle after exhaust change.
 

Hi guys!

I've recently had my catback changed after my JDM TRD Axleback suffered a broken baffle (not sure why either). The midpipe is now a custom 2.5" resonated with a custom 2.5" muffler with quadtips. Am very happy with it until recently I started to notice that there was this buzzing sound going on. I'm also using the Borla UEL headers and the Perrin 2.5" frontpipe and overpipe btw.

How it sounds like: Plastic on metal buzzing, relatively high-pitched. Quite loud especially at higher RPMs (both on free gear and under load). You can hear it as long as you press on the pedal. The more pedal = louder and 'faster' buzzes. On idle it's absolutely quiet. The sound is rather obvious, especially when I'm in a building parking lot or driving close to walls where I can hear my car more clearly - windows down, of course. Definitely not exhaust rasp as I had experience with rasp on my previous TRD setup. On the car jack, the sound seems to come from somewhere near the gearbox or the frontpipe catalyzer. (I've had my headers and overpipe checked and they don't seem to have any issues)

I have had my car sent to quite a few places for inspection: including my dealer, several exhaust shops and a general workshop. I even had my gearbox checked as I thought the sound might have come from there. I can assure you that I've checked all my heatshields and flanges. There are no leaks or anything contacting each other. Most of them pinpointed the sound to come from the catted frontpipe - one even used a stethoscope to determine just that. To test that, I even swapped the frontpipe to a catless one, which actually made the buzz even LOUDER. No loose/broken catalyzer in this case.

One of the technicians mentioned that this sound could be exhaust gas flowing through the thinner frontpipe, which results in this. Since it only exists when the pedal is being pressed, it might have something to do with the exhaust flow. So I have come to the conclusion that this might have something to do with the natural 'resonance' of my entire exhaust setup - which is pretty annoying since I want to hear more of my exhaust notes, not a high-pitched rattle/buzz.

This has been going on since I changed my muffler and mid-pipe - so I suspect the change in exhaust flow might have something to do with that. I'm a newbie when it comes to this since it's my first car, so I would really appreciate if anyone have any opinions/suggestions/advice on this.

What do you think? Is there a way to solve it? MANY THANKS!