Ok, I had this same problem on my 94 s10 blazer when I had it, drove it with the noise for a year before it was totaled. But, it REALLY drives me nuts, and this seems like the place to ask for help.
Ok, mostly when turning left while going over bumps (ever so slightly when going right), I hear a clunking/slapping sound, if I go below 10mph I do not hear it, has to be some momentum behind it to make the noise, It comes from the passenger side only. So I got into the mode to listen to it, and tried to figure out where it was coming from, so I rode in the passenger seat and had someone drive, I could feel it in my feet, but it was really hard to pinpoint what location it was coming from, at times it sounded like it was closer to the floor board, but it also sounded like it was coming from the base of the windshield area by the cowl, I am baffled and rather annoyed by it.

Checked the ball joints, they are not even 2 years old, boots are in good shape, inner and outer tie rods are in good shape as well. Sway bar bushings, control arm bushings were all replaced when the ball joints and tie rods not even 2 years ago.

I was reading up and found a few things it could be but I honestly do not know, torsion bar mount, loose shock bolt, or even the hood hinge, apparently GM did not install a washer causing the hood to clunk (but if it was the hood hinge, I would think it would do it over all bumps, and not just when turning left)

Sorry for my long winded description. hope someone can help.
Thanks

 

*Moved to 1st Gen Tech at the OPs request*

The hood pin washer TSB was only on 2nd gens, not 1st gens. And it wasn't anything GM left out but since I don't think that is really the source of your problem, I won't go into it here.

The only way you are going to figure it out is by getting under your truck and eliminating possibilities. You have two-three strong leads; torsion bar mount being the best lead IMO.

Judging ball joints by the condition of the boot is like judging your engine oil condition by looking at the oil pan. The health of the joint cannot be determined by the exterior condition of the boot. Since these vehicles seem to eat through cheaper ball joints even at stock ride height, that would be the next thing I would check after the torsion bar mount.

 

Thanks, The reason why i was leading more to the torsion bar mount is because when I had my 94, I heard this same sound, right away thought it was the ball joints, So i replaced both upper and lower on the passenger side where the noise was coming from, and the noise persisted. I will go under there with a crow bar and check for play in the torsion bar mount.
Now, if it is the torsion bar mount. is that something that will need to be replaced asap, and how involved is it, its not covered in my haynes manual.

*edit* the upper and lower ball joints on the jimmy are moog, the previous owner kept all receipts and they were replaced early 2010

 

That Tbar mount is a PITA to get out. I was going to put lift keys in but there is some weird bracket that covers the front side and doesnt appear to be of any mechanical value - its in the way of putting on the unloading tool... I gave up and cranked my bars instead. Point is, that looked like a real harsh job to me. Id go over that front end with a crowbar real good. You could also put it up on stands safely and run it up to the speed while you watch whats going on?

 

I could see putting it up on stands and getting it up to speed if it did this noise all the time when driving, but when going straight, its perfectly quiet (even when going over bumps WHILE going straight, its quiet), when turning its usually perfectly quiet. *depending on the speed and how bumpy the turn is*

it has to be a turn with quite a bit of bumps in it to make the suspension work in order to hear this noise. And its only on the passenger side which is odd haha. And it seems to make it more when going left, more so than going right.

I appreciate everyone trying to help me with this though, troubleshooting is the only way to go, and troubleshooting alone makes one go crazy.

Tonight I am going to get under there and look at the mount for the t-bar, and both upper and lower ball joints, and even the shock, and shock mount. I will give an update on what I figure out.

 

my 91 makes a clunking sound when going over speed bumps and making hard turns. it sounds like the leaf springs in the rear like the shackles.

do what i did, go to a field and hang out the back hatch while someone drives and hang ur head under the truck. lol

 

LMFAO! Sounds like what I do when I am getting pictures. I definitely know the sound is coming from the front passenger side, and only when turning and going over bumps, which has led me to think its the torsion bar mount. from what I have read online. I just hate annoying noises. I will figure it out eventually hopefully.
Again, Thanks for everyone helping me troubleshoot

 

Ok, So I checked both upper and lower ball joints on the passenger side, There was no play in either (jacked the jimmy up with the control arm, put a pry bar under the tire and lifted up to check for play on the lower, then grabbed the top of the tire and moved it in and out to check for play on the upper)

Then I moved on back to the torsion bar mounts, Is there supposed to be any play in the t-bar mounts at all, There was a tiny bit of play there, Not even close to as bad as the video that is on youtube of the 88 or 89 s10 blazer, but i noticed some play.