wheel vibration

[rh71]

I've mentioned this before but I need to revisit it. At 60mph+, depending on how quickly I accelerate, there's a bad seat vibration. Doesn't matter if the sport button is on. Happened before I got spacers too. You can't miss it if you're inside and if you look at the headrest as the vehicle is moving, it's shaking. It's not in the steering wheel so I'm assuming it's in the rear wheels.

I can't imagine this is uncommon with the E70 feeling every little bump in the road. Am I alone here? I've been battling this issue since I changed from my stock 19s to rep 20s nearly 3 years ago. Thing is I've had the rims and wheels changed with new ones more than once, and road-force balanced, regular balanced, spun for symmetry, you name it. Because of this happening only above 60mph, is it only a balance issue?

I know I'm not the only one on Toyo Proxes STII nor replica 214s (or any replicas at all). I feel very faint vibration in my dad's minivan on the same roads so I know the roads are a factor, but with the E70, it ampliflies the imperfections. How come nobody else complains of this? I'm nearing the end of my warranty and I want to be absolutely sure there's nothing else mechanically wrong with the vehicle (2 years ago they checked and claimed there wasn't).