Feel/hear clunk noise 1X or 2X when aggressively accelerating from 20mph-60mph

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LTZ 4WD I don't hear the noise or feel any vibration if casually accelerating. When it occurs definitely feel it directly under driver's seat. I was thinking U joints but maybe CV joint or unfortunately front differential. Has 170000 Mileage on it. Any ideas to point me in right direction or ways to diagnose or isolate for trouble shooting?