If you guys can find threads on this, links would be appreciated; I have yet to locate any though.

Ok, so I don't recall ever feeling this vibration prior to this year. Over the winter I swapped out the clutch, flywheel, diff, gears, and rims/tires (NT03s). I think I swapped the coils in late June, and I can't remember for sure if it was there prior or not (I believe it was, but not 100%).

As I'm driving anywhere above 50mph, I get a pulsing vibration as in...it's not there for .5 seconds, then there for .5, then not, etc. I believe it is coming from the rear as the steering wheel is unaffected. There is no noise to speak of and it gets worse as speed increases, but it's difficult to say if the cycles get closer together or not. I added 5mm spacers to the rear and the vibration got worse; I removed them and it improved to where it was prior.

My best guess at this point is a bearing, especially given the Z's apparent reputation for weak ones. I just want to check here to see if anyone has another. I don't know if it's related, but last year I had a clunking coming from the rear end under hard acceleration; the shop I took it to couldn't figure it out and it went away on its own after a week or two.

Thanks in advance.