This noise happened everyday, all the time. I brought this to the dealer, to no avail - it’s a 2018 Yukon Denali 6.2 with 2k miles and has done since 22 miles on the odometer
My seal appeared to be fully seated as well, however there was some play in the seal on the steering shaft. I ended up purchasing a new boot (p/n 25815601) and white lithium grease from Amazon ($35 total). I removed the 15mm bolt from the steering shaft, and removed the 3x 10mm nuts from the boot on the firewall, and removed.
Looking at the old boot, it is different - looks like a different mold on the multi-layer rubber. I also noticed a fold on the rubber where it meets the firewall.
I took the new boot and packed it with white lithium grease, perhaps not necessary, but this noise is extremely annoying. I installed the new boot, catching all the extra grease that was pushed out. Made sure it was absolutely flat against the firewall (it was getting caught on the insulation - had to move it around to seat properly). Installed nuts, torquing down until the seal was pushing firmly on the firewall, and installed the 15mm bold in the steering shaft.
No Noise!! It’s completely gone!! Worth every penny and the 30 min to change out.
