I don't know........... maybe I've just been lucky or something!! but I've run 3 geardrives in my hotrods........ and never had any problems or noticed any change in harmonics, vibration, or even any change in fluxuation with a timeing light on the degree marks on the harmonic balancer. And I'm getting ready to slap one on my 23T this comeing weekend. The noise dosent bother me, but I can understand how it can get to some people.
This is just my personal opinion........ which with $0.25 will almost get you a bag of chip's. D