Not sure I'm going to be able to solve the problem, but as a TNT owner with flywheel thought I would at least try to help. Firstly, it is highly unlikely that this is a grounding problem as the flywheel is not electrically connected to anything. I can't help but wonder if the belts might be the problem as the addition of the flywheel increases the strain/torque on the belts; perhaps leading to some intermittant slippage? Did you get all new belts when you added the flywheel? One thing you might want to try is placing all the belts back in the talcum powder, then back on the turntable and see if this improves things.
Hope this helps, but if it doesn't, VPI is excellent about supporting their products. Don't hesitate to email or call them. Let us know how this turns out.
Hope this helps, but if it doesn't, VPI is excellent about supporting their products. Don't hesitate to email or call them. Let us know how this turns out.