Repower Athearn H0 CF-7

[Green_Elite_Cab]

... Is is the flywheel itself that isn't turning right, or is it just not sitting on the shaft correctly?

The problem is the motor-flywheel-assembly. To do it the right way the flywheel should be mounted at the manufacture site and they should balance the whole assembly prior selling them. It is not a good idea to sell the motor and two flywheels as separate parts and hope the assembly will be balanced after they are glued together by the customer.
The shafts have a problem with length and mass. The generic one have a much greater mass then the standard shafts and therefor another potential unbalance.

However, you should read my comments with an understanding that I am much more sensitive to any kind of noise than most people.

LOL! Oh the joys of aftermarket parts. Thats why at my job, we try to use Genuine GM parts when we can on our diesel rebuilds. I was only curious because i have a few of the products, and hadn't noticed this issue. Now i'm starting to wonder if the wobble in my E60 is all from that long drive shaft, but whatever, those things wobbled anyway (their top legal speed went from 120 mph to 80 because of this wobble).

I'm surprised they don't test these things or match them up somehow.

but yeah, even without the noise sensitivity, unless your running traction, you don't want the sound of a motor humming to loudly!