2018 Yukon Denali grinding/knocking noise

[Engineered]

Hi Everyone, first post, but a long time user of the site. I’m at my wits end with a noise, we will call it a noise for now. Hoping to muster the wisdom and knowledge of the many experts. Please

Truck has 84k miles, mostly a grocery go getter.

Here is the situation, when going down hill at approx 30mph, and then braking while going over some mild bumps. I get a knocking or slapping type noise and feel. It almost feels like a warped rotor or bad ball joint. It feels like it’s coming from front drivers side. Can feel it in the floor board.

Here are the parts I’ve replaced.
All GM parts.
Both front hubs, Rotors, pads, calipers, shocks (Arnott), drivers motor mount, sway bar bushings, end links.

I’ve checked the tie rod ball joints and control arm joints. Grab tire at 12 and 6. Then 3 and 9. Everything is tight.

When I grab the axle’s they do have a little movement in and out. Is this normal?

Thank you in advance, any and all help ideas appreciated.

 

[Fless]

Transmission mount? Crossmember bolts loose?

 

[ivin74]

Are you referring to the front axles or the axle from the transfer case to the front differential?

Have you checked the drivers side control arm bushings?

Shake the exhaust by drivers side catalytic converter? When they go out some times the internals break up and make noises.

 

[Engineered]

Thank you for the replies.
I have not checked the trans mount or cross member. Will add that to the list this week.

For the axles i am referring to the drivers side cv axle. I’m familiar with the rattle from a bad cat, this noise doesn’t seem to match that. Control arm bushings have been checked, put a pry bar to them just the other day. They are tight and just re-torqued them. 140 upper and 129 lower.

Another thing to note is that this noise is intermittent. When going down hill on a smooth road, even at highway speed and braking the truck won’t make the noise. It’s just this one spot, and figures is the route we take to bring the kids to school.

 

[ivin74]

Another thing to note is that this noise is intermittent. When going down hill on a smooth road, even at highway speed and braking the truck won’t make the noise. It’s just this one spot, and figures is the route we take to bring the kids to school.

Are you coasting down hill (not accelerating). Is the sound a humming/gears noise?

 

[Engineered]

Yes coasting down hill. It is not a humming/gear noise. I would equate it to a badly warped rotor noise.

 

[Engineered]

Bump

 

[tom3]

Rotate tires?

 

[Doubeleive]

Bump

I would be inspecting everything else under the truck, these things will fool you and throw noise around and they are good at it. the rear can be doing something and it will totally sound like it is from the front.
the very slight movement of the cv axle is normal, same for the rear axles.
maybe also take a look at the body mounts

 

[Fless]

One thing I neglected to mention is the front diff mounts. Bushings should be checked.

 

[Engineered]

Thank you, will check them asap.

 

[ivin74]

Yes coasting down hill. It is not a humming/gear noise. I would equate it to a badly warped rotor noise.

The exhaust flange is right below the driver floor board, it wouldn't hurt to check and see if the gasket blew out.

 

[ivin74]

One thing I neglected to mention is the front diff mounts. Bushings should be checked.

^x2

 

[Engineered]

Thank you. Making a list for this weekend.

 

[Engineered]

Reporting back. Went under the truck and tried to pry on the rack and diff mounts. Retorqued. All seem tight. Noise still there.

While I was under there I grabbed the stub shaft that connects to the CV Axles. The stub shaft on passenger side has a small amount of in and out movement and no up down left right movement. The drivers side has the same in and out movement, but also has a couple millimeters or about an 1/16th to an 1/8th of up down left right movement.

Thoughts on this?
Thank you

 

[Geotrash]

Reporting back. Went under the truck and tried to pry on the rack and diff mounts. Retorqued. All seem tight. Noise still there.

While I was under there I grabbed the stub shaft that connects to the CV Axles. The stub shaft on passenger side has a small amount of in and out movement and no up down left right movement. The drivers side has the same in and out movement, but also has a couple millimeters or about an 1/16th to an 1/8th of up down left right movement.

Thoughts on this?
Thank you

That's quite a bit of play in the bearing. Should be tight with no up/down movement. Slight in and out movement is okay. Hard to say if that's enough play to be your problem, but it does tell me that you have a worn bearing on that side of your diff that should be replaced anyway. You can do it on the bench, but for differential work on these trucks, I like to take it to a shop because I'm getting old and lazy.

 

[Engineered]

Thank you, I’m going to swap out the bearing and seal. Cheap enough.

 

[Engineered]

Solved. It turned out to be the differential mounting bracket bushings. Decided to replace them as a Hail Mary pass as the bushings looked fine. In addition to fixing the noise described earlier, it also fixed my driveline clunk coming to a stop and accelerating.