Like the title says -- I installed some GT500 mufflers and now I'm getting a loud buzz from the rear of the car under hard throttle -- around 3k RPMs. Sounds like 2 hard materials (maybe metal) vibrating against each other at high frequency.

It always happens at the roughly the same RPM and only hard hard throttle. It seems that there's a very specific sound frequency that creates just the right harmonic to make it buzz. The sound also doesn't sound like it's coming from the muffler area; it sounds more like it's on the body of the car. I'm thinking this was something that has been on the car since it was manufacturered but the stock pipes didn't resonate at the right frequency to make it happen.

Anyone else seen this? It's very hard to debug because it only happens while I'm driving and under hard throttle.

 

Sounds like one of two things: the pipe/muffler is rubbing somewhere, or you've got a leak.

 

sounds like one of the bolts is loose holding the mufflers in place, i have the same issue but it only happens to me at low rpms. im just to lazy to tighten them down more

 

If your car were older I tell you it was the heat shield making that buzzing, fluttery sound but yep... Crawl under there and tighten that loose @ss bolt with authority.

 

Fairly certain it's not a loose bolt, but I'll double check.

And actually heat shield is not a bad theory - it does kind of sound like that.

 

Being you worked on the exhaust, you need to check the entire system to be sure nothing got shifted a bit.

 

My main concern is that this might be something in elsewhere on the car that was always loose but never resonated at the right frequency to make a noise. It doesn't really sound like it's coming from underneath the car but I could be wrong.

I'll double check all the exhaust and see if I shifted something.

 

Something is loose or rubbing, make sure that there is no metal vibrating against frame, suspension, axle, etc.

Agreed with pretty much everything else everyone said

 

+1, I had a similar issue after trying to fix an exhaust leak where I had a bolt where my x-pipe and cat connected that I had touching the frame, made for an interesting ride till I fixed it.

 

In one article about the 13500 upgrades they mentioned with the dual exit exhaust, although it uses the same muffler as the older ones the dual outlet got rid of the mad cat hiss in the older exhaust at higher rpm because of less back pressure. Not sure if that is what you are hearing with the 5.0 but just a option. Good luck!

 

Well I feel like a complete dumba55. After a long day of laying on my back to install an MGW shifter and then the GT500s, it seems that I left a bolt halfway tightened I must have tightened it halfway then went to align the muffler and never came back to it. Anywho -- there was a washer dancing on the half tightened bolt and creating the buzz...

Fixed now! Thanks for the suggestions guys.