I drive a 2018 Sierra cc SLT 5.3, this is the second new GMC I’ve bought, my first being a 2016 dc SLE 5.3. After roughly 2000 miles of driving my 2016 I started hearing the DI system “tick” coming through the drivers side foot well, I’m a 10 year diesel tech and my gut told me it was an exhaust leak... after 6 trips to the dealer 6 loaners hp fuel line tsb’s performed and everything exhaust related gone through with a fine thoothed comb this issue was still present. I’m a quiet type of driver most of the time, I enjoy reflecting on what the work day will bring while listening to every sweet sound of a fine working machine while Im driving to work. This noise freaking drove me nuts!!!!!! Finally after 8 months of crossing the 2000 mile mark I had spent hundreds of hours scouring forums and I ran across a guy that had an engineer come to his dealer verify the noise and instruct the replacement of the drivers side exhaust manifold and the steering shaft boot, so I asked my service advisor if he would replace the boot on my truck and he agreed... noise was gone for about a month then came back intermittently.. if it hit a certain bump it would start. I’m now a 35000 miles on my 2018 and the noise has started... after going this long I thought they had updated the boot and fixed the issue!! I am so happy after reading some forums to see that GM has recognized this issue!! I had found the TSB and read it over earlier this evening and I decided I climb under the hood of my truck and try to find where the defect of the boot is or in other words where the gap was at that is allowing engine noise into the cab, I found that instead of updating to a positive lock seal (lip seal) like found on an engine crankshaft or a rear end pinion seal they used an o ring of sort made into the boot that is roughly .030 larger than the steering shaft WTF!!!!!!! Their update to get you out of warranty was to pack it with lithium grease like you guys are doing and let er bump... good for about 30000 miles. I will include pics of mine inside and out untouched factory condition and you can see the air gap where the lithium grease has give way to mileage and allowed the noise to intrude into the cab.. with all this bad news I believe I have conjured a solution in my discontent, tomorrow I’m going to install a hose clamp around the o ringed portion of the boot where you see the air gap in my pic to effectively shrink the seal to the size it should have been manufactured. I will give an update on the results, good luck to you guys, I feel your pain!