Hello!
On this particular model vehicle, the usual cause of what you describe is torn or deteriorated torsion bar mounts (GM calls them "cushions")
These are rubber blocks located where the crossmember that the front torsion bars are mounted to attaches to the vehicle frame, in the general area of the drver's seat underneath the vehicle. If you go under the ruck with a pry bar and inspect this area, you may find that by prying in the area where the rubber cushiopns are located you can separate them enough to see torn rubber; if so, this is probably the source of the noise you are hearing and they will need to be replaced. The parts are not terribly expensive (around $20 per side), but a special tool to unload the torsion bars is required to install them so this is a job best taken in to a repair shop.
I hope this is helpful; if so, an accept would be most appreciated! thanks!
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