Exhaust Valve Noise - 2015 5.3L 4x4

ember1205 · November 4, 2021

2015 Crew Cab 4x4, 5.3L, almost 90k.

Ran into an issue where the truck would "bark" on downshift with the engine under some load. Example: Drive along at 30-40MPH on a level road, truck settles in an drops RPM's to "cruise" along. Road slopes upward into an actual hill (not just a small incline). Push down on the accelerator to maintain speed, truck drops at least 2 gears. At the -exact- moment of the downshift, there's a sort of 'barking' noise emitted which can vary in duration and volume. The very first time it happened, I was speeding up to move to the left lane on the highway at the moment I was starting to climb a grade. I was traveling around 60MPH and the truck dropped at least two gears on the downshift. The noise was fairly loud and lasted 1-2 seconds in length.

Dealer has indicated that the issue is related to a mechanical valve at the rear portion of the exhaust (directly in front of the muffler) and it's part of a complete muffler system. In other words, the only way to correct it is to replace the entire exhaust which simply isn't happening, at least not at dealer prices. They've also stated that the valve can't be lubricated in any way to address the issue. I've seen the valve they're talking about, and that entire area is reasonably corroded after 6 New England winters of driving.

Thoughts on how to address this other than a complete exhaust swap?

MikeBMW · November 5, 2021

15 hours ago, ember1205 said:

Thoughts on how to address this other than a complete exhaust swap?

Here is a thread about the flapper valve, might be of help?
I have no direct knowledge to guide you, just offering assitance.

ember1205 · November 5, 2021

Thanks. I wish I could figure out if that part were serviceable in any way without replacing the entire assembly. Dealer says it can't be lubricated or anything.

M1ck3y · November 7, 2021

On 11/5/2021 at 7:02 AM, ember1205 said:

Thanks. I wish I could figure out if that part were serviceable in any way without replacing the entire assembly. Dealer says it can't be lubricated or anything.

Anything you put on will burn off.

JimCost2014 · November 7, 2021

Was listening to the "flapper valve" in our 2016 LTZ Tahoe today coming down Highway 410 from Crystal Mountain.

Every time it switched from V4 to V8, and back, you could here the "squeak" as it operated. Nothing says "world class build" in a vehicle with a MSRP of $75,000.00 like a constant annoying noise during your trip

ember1205 · November 7, 2021

14 hours ago, M1ck3y said:

Anything you put on will burn off.

What about something dry like a graphite, though? I realize that any liquid-based lubricant wouldn't hold up, but wasn't sure if there might be something that wouldn't be affected.

It would have been nice if they had made all of the valve components out of stainless steel to prevent the rot/rust problem that has led to the squeak.

Dealer wants $1400 to replace the muffler because that valve is part of the complete system and apparently not available as an individual piece. I can buy the part for about $450 and have my mechanic put it on for under $200. No way the dealer is getting more than double that for the same repair. If I decided not to do anything about it at all for six months, maybe I'll do the repair myself next spring when I won't be freezing to death under the truck.

M1ck3y · November 7, 2021

33 minutes ago, ember1205 said:

What about something dry like a graphite, though? I realize that any liquid-based lubricant wouldn't hold up, but wasn't sure if there might be something that wouldn't be affected.

It would have been nice if they had made all of the valve components out of stainless steel to prevent the rot/rust problem that has led to the squeak.

Dealer wants $1400 to replace the muffler because that valve is part of the complete system and apparently not available as an individual piece. I can buy the part for about $450 and have my mechanic put it on for under $200. No way the dealer is getting more than double that for the same repair. If I decided not to do anything about it at all for six months, maybe I'll do the repair myself next spring when I won't be freezing to death under the truck.

You would have to find a lubricant that is designed to survive probably a minimum of 500 degrees.

That being said, you could try applying an anti seize/rust killer like corrosion free, rust check etc. One that's designed to penetrate and break up the rust.

Let it sit for a couple days and do it's work. Worth a shot anyways?

I imagine it's the outside spring and/or connection at the housing thats squeaking. Probably no need to try and spray the inside.

Edited November 7, 2021 by M1ck3y