Please help!! Diagnosing a noise...

[awphillips93]

Hey guys, I need a little help and I figured you guys are my best bet.

A few days ago, a buddy and I were looking for a fishing spot my brother told me about. It included a little off-roading, and next thing you know, we decided to just keep driving around. When we decided to leave, we thought about just driving over this berm separating us from the road. It was covered in tall weeds, but I figured I could make it. Note that I am driving a stock extended cab, long bed Silverado 1500 (2011).

Turns out there was a bolder hiding in the weeds that I got stuck on, front wheels off the ground and everything. I was able to scrape myself off and drive away, only I had this strange buzzing/rattling noise now coming from just under the floor beneath my feet. As I drove around trying to trouble shoot the noise, I learned the following things:
- Noise happens when accelerating
- Noise does not happen while coasting or braking
- Noise happens after starting the engine cold
- Noise does not happen after starting the engine warm or during idle (once warm)
- Noise does not happen when revving the engine in neutral

I looked and wasn't able to really see anything except for a small dent in my exhaust pipe on the driver's side before the cat. What I'm thinking, then, is that this is an exhaust issue and that the dent is causing some type of (hopefully harmless) resonance. Could that be it?

Thanks for any help you guys can give.

Cheers,
Alex

 

[LWD601]

Exhaust leak maybe. Is it possible that it's a small enough leak that once the engine warms up the metal expands enough to close up the opening until it gets more pressure from acceleration?

 

[dnorrell]

I had a similar noise, at least from what I am reading, when I put a y-pipe on a previous Jeep JKU during lift install. Turns out the pipe wasn't quite right and was causing a small leak at one of the junction points (can't remember which). It could be that the exhaust got whacked enough for a dent and may have compromised a seam somewhere up or downstream. Total guess. Hope you get it sorted. How sensitive is your sniffer? Can you pick up any hints of exhaust with the window down?

 

[Sock Puppet]

Are there any heat shields on that exhaust system? One of them could have been knocked loose/askew, which will cause some strange noises and vibrations.

 

[awphillips93]

There could be a leak somewhere. I gave it a quick and dirty inspection afterwards (without a flashlight, mind you) to see if something had been knocked loose or if a seam got compromised. Didn't see anything super obvious, just figured/hoped the dent is disrupting airflow and causing resonance. I may have detected exhaust smell, but I will double check for that after work.

No heat shields in the vicinity, so I don't think that is it.

You guys think that it's most likely an exhaust leak and not just a dent? That would make sense. I just want to know what to throw my time/money at first. Thanks for the help so far, it's definitely appreciated.

Alex

 

[awphillips93]

Just went out to the parking lot to double check, no hole where the dent is. Also upon second inspection, the dent is too small & smooth to create any serious disruption in airflow to cause a noise. What I'm thinking is that I'll have to tighten the bolts where the cat bolts up to the headers, that seems to be where the noise is coming from and it's the only "seam" in the exhaust in that area. I'll cross my fingers and post back if that fixes it.

Alex

 

[4x4junkie]

A simple dent by itself shouldn't cause much issue unless the dent is so severe that the tube is collapsed almost flat.
I assume there hasn't been a change in the engine's output performance, or the Check Engine light coming on?

I would suggest drive it up onto a set of ramps, then just get underneath there and start inspecting everything. Push up & down & side-side on the exhaust tubing while thumping on things with your hand to see if you can replicate the rattle.
I've had exhaust shields start buzzing/rattling on mine in the past... All that holds them on (at least on mine) were small spot-welds at each corner to the tubing. It doesn't take much to break a weld or two and have it start rattling.

 

[gtbensley]

Heat shield or loose exhaust sounds about right.

 

[rayra]

LIkely the hit that caused the dent shifted the pipe at one of the bolted unions, resulting in either a leak or something loose to rattle.

 

[awphillips93]

Correct, no change in performance and no Check Engine Light, either.

 

[Buliwyf]

Exhaust leak at the header/head. Not the dent.

 

[justcuz]

After laying the weight of the truck on the exhaust system, it may have tweaked it just a bit. Start at your exhaust manifolds and work towards the dent. Snug every bolt or nut back up, should fix it.