It won't be driveshaft if it's RPM related. Mine does that too sometimes and I just assumed it to be something in the B&M shifter. Been doing it for over a year and nothing has failed. An incorrectly machined flywheel would cause the clutch to burn out faster but I don't think it would be vibration related.
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'91 LX Hatch, 17 ROH ZR6's, lowered, 3.73's, offroad H pipe, SN Cobra cat-back, ASP pullies, 14° timing, C&L 76mm MAF, 170A 3G, B&M Ripper on a T5
1991 LX Hatch 5.0L