Do you have a G80 locking rear end? If so, does it make a popping sound when your taking turns?
If it does, it sounds like your rear end could need some fixing. I had a 1990 Full Size cab in a half long bed with the G80 on it & it blew on me. Thankfully, it was covered under warranty & I have no idea what it would cost to repair one now. Don't think that it is too much.............
If it isn't that, then I don't have a clue. It's just one of those things where I would have to drive it to hear it to maybe figure it out........
Or you could just take it to the dealer where they would tell you that "they all do that....it's normal

darn dealers.........
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2003 TrailBlazer EXT 4X4 NorthFace Edition. Silver Green over Pewter
Every option minus the DVD 4 a MoonRoof.
5.3 V8 3.73 Locking Rear.
Performance:
TrueFlow Air Intake
Granatelli Mass Flow Air Sensor
FlowMaster 70 Series SUV Muffler
Predator Power Programmer
Airaid Throttle Body Spacer
Misc.:
Super White headlights 80W & 100W
Fog Lamp bulbs
Billet Grill
XM
Tekonsha Prodigy Brake Box
Valentine 1 Radar
Line Of Fire 49" L.E.D Brake Light