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.