Exhaust Flapper Whistle

19Sierra · May 17, 2020

Does anybody else notice a whistling noise coming from they're exhaust? Since the warmer weather I've been driving with the windows down and started noticing it everytime I accelerate. Very noticeable when something is along side the truck. I have the 5.3L with single side exit exhaust.

I wired the flapper before the muffler open and the whistle completely disappeared. Only difference I notice with the flapper open is that the whistle is no longer there. Just curious if there's a problem with the flapper on my truck or if they all do it.

Thank you.

CamGTP · May 18, 2020

I noticed it on my truck and my parents truck. They are both 2016's but the flapper stuff is all the same.

I have an aftermarket exhaust now so that's all gone.

19Sierra · May 22, 2020

On 5/18/2020 at 12:14 AM, CamGTP said:

I noticed it on my truck and my parents truck. They are both 2016's but the flapper stuff is all the same.

I have an aftermarket exhaust now so that's all gone.

Guess we are the only ones who noticed it. Lol after having it wired open for almost a week the only difference I can tell is that it doesnt whistle anymore. Doesnt seem to do anything else.

jnissen · May 23, 2020

Was the flapper a one way valve for deep water? Sorry but new to GM trucks.

19Sierra · May 23, 2020

5 hours ago, jnissen said:

Was the flapper a one way valve for deep water? Sorry but new to GM trucks.

From my understanding and from watching this video it appears that its purpose is to quiet idle noise. I cant tell a difference in noise with it open or closed. If it has another function than I would be interested to know.

CamGTP · May 25, 2020

They say it also helps drown out the AFM/DoD system because the valve gives it another thing to interrupt the exhaust pulses.

JohnH4260 · January 12, 2021

On 5/17/2020 at 2:52 PM, 19Sierra said:

Does anybody else notice a whistling noise coming from they're exhaust? Since the warmer weather I've been driving with the windows down and started noticing it everytime I accelerate. Very noticeable when something is along side the truck. I have the 5.3L with single side exit exhaust.

I wired the flapper before the muffler open and the whistle completely disappeared. Only difference I notice with the flapper open is that the whistle is no longer there. Just curious if there's a problem with the flapper on my truck or if they all do it.

Thank you.

How did you wire the valve open?

19Sierra · January 12, 2021

32 minutes ago, JohnH4260 said:

How did you wire the valve open?

JohnH4260 · January 12, 2021

14 minutes ago, 19Sierra said:

Thank you for the photo. What gauge wire did you use?

19Sierra · January 12, 2021

16 minutes ago, JohnH4260 said:

Thank you for the photo. What gauge wire did you use?

I think I used .045 or 1/16". I recommend using stainless so it doesn't rust. If you have a welding supply store near by just stop in and ask for a piece of .045 or 1/16 stainless filler metal.

JohnH4260 · January 13, 2021

On 1/11/2021 at 7:51 PM, 19Sierra said:

I think I used .045 or 1/16". I recommend using stainless so it doesn't rust. If you have a welding supply store near by just stop in and ask for a piece of .045 or 1/16 stainless filler metal.

Thank you.