I'm posting this to help others in the future since I found just about zero information on this issue and part failing from my forum searching and googling.
TLDR version:
If you have a rattling and clicking noise in your steering column while driving, it may not be the typical worn out rag joint or steering column bearing, check the tulip joint on the upper intermediate steering shaft.
Full Version:
I bought a 2002 2 door 2wd blazer late 2017 with only 60k miles. Around 65k miles I noticed there was a slight clicking/rattling noise in the steering column when driving in a straight line over 65mph with the steering unloaded. The sound would go away as soon as your turned the wheel slightly to the left or right, or the steering became loaded from road forces. This translates to a few seconds of rattling followed by a few seconds of silence, repeated over and over, obviously annoying as fuck. There is/was minimal play in the steering wheel on this vehicle, enough to be expected in a vehicle with 69k miles.
Below is a video of the noise, it was easily recreated by simply shaking the unit.
https://youtu.be/TP76d6sTz9AI then lowered the vehicle in 2018 with Z87 (blazer Xtreme) coils and leafs, drop spindles, UMI upper arms with tall ball joints, and JTR blocks. The new front suspension setup increased the stock camber from 4.5deg to a more aggressive street/track setting of 6.5deg. This increase in camber made the clicking rattling noise even more noticeable as the increased camber made for even less of a load when driving in a straight line at higher speeds. At this point the noise was too much to ignore.
After weeks of researching what could cause the problem, all I could find was the common rag joint wear/failure that can introduce play. I didn't think it was that since the noise was present inside the cab, also the rag joint on this vehicle, at its current 69k miles, is still solid with little to no play. I then found out that in full size GM trucks typically the plastic steering column bearing goes bad, and that also introduces the exact same clicking rattling clunking noise inside the cab. A part number search showed that my 2002 blazer utilized this same bearing part number as the 99-07 fullsize trucks, so I ordered a replacement off amazon for $20.
This past weekend I removed the steering column to replace the bearing but found the original unit to be solid with no play. At that point I removed what is called the upper intermediate shaft, which has a tulip joint on it, upon shaking it by hand I realized this was the problem as it makes pretty much the same clicking noise that I experienced while driving.
The upper intermediate shaft, with the tulip joint at the end, is only a little over a foot long, and is actually the middle section of the steering column/shaft assemblies. It slides into the lower intermediate shaft which is the part that has the rag joint and is attached to the steering gear box. Directly above the tulip joint on this part, is the steering column assembly which it bolts on to. The two intermediate shafts do not bolt together and just slide into each other (so that it may collapse in a collision). Apparently in earlier years of s10s this joint is located in the engine compartment in front of the firewall, whereas on my blazer it's located inside the cab just in front of the firewall. I'm not sure which year the switch over was but I imagine they could go bad either way. Removal of the shaft required me removing the steering column, but the lower intermediate shaft (with the rag joint) did not have to be removed.
The GM part number was 26056116 and I was able to find it for $85-100 from various gm parts websites. The aftermarket units from Autozone and others were $250-$290, so I'd stick to the oem while still available.
The replacement cured the issue 100%. Despite the tulip joint having been bad on the old unit, I did not notice any improvement in steering wheel play after its replacement, but as mentioned earlier, there was very little play in the steering to begin with.
