GM Borla Making Strange Noise

ShamrockShooter · May 17, 2017

Wanted to start a new thread just about this noise. I have the new version flapper GM Borla on the 5.3 with about 1000 miles on it. The last week or two it has started making a secondary noise that is hard to describe but doesn't sound normal. It has this rhythmic echo/vibration/fluttering/humming sound. It doesn't sound like a direct metal on metal or loose nut kind of noise. I checked all the clamps and brackets but nothing is loose or touching. When I knock on the muffler it doesn't sound like anything is loose in there. I had a bad flapper on my stock exhaust so I know what that sounds like so I don't think it's the flapper. Although I may try pinning the flapper open to trouble shoot, but it's not as easy as the old flapper design.

I only notice it at low rpms on highway or slow speeds 1000 to 1300 rpms. It has a rhythmic pulsation to it like it's matched to something cyclical in the engine. I can hear it even louder with the rear slider open.

Anyone else have this issue or noise that can tell me what might be causing it? I don't want to call Borla and have them start shipping parts until I figure out what is causing the noise.

Thanks

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Edited May 17, 2017 by ShamrockShooter

Krusty · May 17, 2017

I assume your are running around in V4 - If so try M7..........

ShamrockShooter · May 17, 2017

V4 is turned off with range

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Krusty · May 17, 2017

V4 is turned off with range

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Well no reason for a flapper then.........

ShamrockShooter · May 17, 2017

Well no reason for a flapper then.........

Yeah in hindsight I would have just bought the version without it. But I wanted the option for v4 that didn't sound that bad if I chose to turn v4 back on.

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slee3247 · May 18, 2017

Sounds to me like some sort of issue with the flapper..but I've been tuned and flapper-less since the dealership lot

ShamrockShooter · May 18, 2017

Well I wired open the flapper which is hard to do with the new design. It has a really stiff spring on it. I only made a quick trip around the block, but I think the strange noise I'm hearing is still there.

I pulled my range afm to see what v4 sounded like with the flapper clamped open. I would say the new flapper on the borla reduces the v4 chop by maybe 15 to 20%. It still sounds like a farting Subaru boxer engine. Range will be going back in.

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camcamaro1991 · May 18, 2017

funny, I cant even hear my exhaust... not until I roll down my windows or full throttle. sound deadening FTW!

Edited May 18, 2017 by camcamaro1991

CDNSS · May 18, 2017

Bummer you would think the GM Borla system would have this figured out .........I went back and forth on Borla or Corsa in the end went the GMPP "performance exhaust" ( made by Corsa) on my 2017 6.2 3.5" system huge 28" muffler no flapper no resonator only have 700 miles on truck so far but when in V4 at low speeds you can hear it if you listen for it but very mild no issue IMO at 50 mph and higher in V4 no helicopter sound at all

Hope you get it figured out

ShamrockShooter · May 18, 2017

So it's definitely not the flapper. Drove all the way to work with it wired open and its still making the noise.

Here is a video at idle from rear slider looking down between bed. Might have to turn volume all the way up. Its a cyclical metal humming echoing noise. The same noise can be heard at different rpms under say 1700 when cruising along. I'm starting to think it's something loose or vibrating inside the muffler.

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bndawgs · May 18, 2017

you sure it's not something else with either the driveline, axles, or tires?

ShamrockShooter · May 18, 2017

you sure it's not something else with either the driveline, axles, or tires?

Well not 100 percent sure. But it makes the noise when parked idling too, so that eliminates a lot of things.

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bndawgs · May 18, 2017

Well not 100 percent sure. But it makes the noise when parked idling too, so that eliminates a lot of things.

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that's true. when it's idling, have you climbed underneath to listen around? maybe pop the hood too?

ShamrockShooter · May 18, 2017

that's true. when it's idling, have you climbed underneath to listen around? maybe pop the hood too?

Yeah did a bit of poking and prodding. Heat shields are all tight, nothing else looks loose. The deep base sound of the borla makes it too loud to hear other rattles from underneath. That's why I took a video from rear slider.

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camcamaro1991 · May 18, 2017

I don't hear anything, if your using a phone mic... its not going to pic up sound very well. put the stock exhaust on, you need to do your due diligence and remove/eliminate variables.