Intermittent Vibration/Rattling at certain speeds. All fixes so far have helped none.

[mdurm]

Hey guys.  Hope everyone is having a great Friday.  

 

I have a 2017 Silverado with a 4" Rancho lift and 35" tires.  I'm kind of at a breaking point with this noise.  It's a vibration/rattling that's pretty deep sounding.  I'm not saying this in jest, but it sounds like a mechanical fart if there was one.  It's almost always at 40-45 and 65-75 MPH.  It is at its worst going uphill with light acceleration.  It will feel like the truck is stumbling and you know it's coming, then the noise will start in little spurts with space in between, or the noise will be continuous if you stay at the exact MPH with foot stable on the pedal.  As soon as you break or let off it will cease.  The longest continuation of the noise will be 5-10 seconds I'd say.  I feel it through the gas pedal and sometimes the steering wheel.  It's not like the whole trucks shaking.  The noise happens at the exact same places at the exact same times every day going to/from work and other places.  Since the issue started I've had spark plugs replaced, transmission flushed, maintenance with break pads and rotors.  Nothing has fixed it. 

 

I have some videos attached that should help.  You'll hear intermittent vibrating/rattling/shaking.  Also, one one you will hear a wo wo wo wo noise.  These were taken in the cab where I stuck the phone as close to my feet as I could.  It sounds more prominent and deeper when you are in the cab.  I would appreciate any suggestions/insight if possible.

 

Thanks

 

[Snowcamo]

Checkout the vid in this post. Sorta sounds like what may be your issue. 

 

Pinion angle.

 

https://www.gm-trucks.com/forums/topic/153186-shake-or-vibration-issues/?do=findComment&comment=2650292

[superdave160]

As I read your post, it reminded me of something that I have experienced with my 2017 Silverado.  I do not have a lift on my truck, only the front end leveled.  I also have factory size tires.  If I'm driving with the transmission in 6th gear and the torque converter locked, and then ease down on the gas pedal, my engine will start making a "rattling" noise.  If I ease up on the throttle it immediately goes away.  I have found that if I use higher octane gas the noise is less likely to occur.

 

In the last year, I have had a DOD delete, bigger camshaft installed, and an L86 intake manifold and throttle body installed.  I took the truck to a local shop for tuning services, and that is when this rattling noise appeared.  In fact, the first time that I drove the truck, not only was there a rattling noise, but the truck also "jerked" when the noise was present.  I found that the intake manifold was not torqued properly and there was an air leak in the intake tube (the mechanic managed to crack it).  After fixing those issues, the problem was still there but greatly diminished.  I also purchased an Edge CTS3 display so that I could monitor engine data in real time.  What I found was the noise was occurring when the engine spark timing was severely reduced.  I monitor knock ****** on the CTS3 display and the noise is often accompanied by an indication that the timing is being reduced due to knock.

 

Here are a couple tests that you could do to rule out/confirm that the issue is your engine.  First, fill up with higher octane gas and see if the issue is reduced.  Second, drive your truck until it is in one of the speed zones that you mentioned, then slowly ease down on the accelerator and see if the noise either appears or gets worse.  If it comes and goes with pressure on/off the accelerator, then it may be your engine. 

 

I ended up modifying the tune myself and the truck is much better now.