Yep, sounds like an R-200 to me!
Mine is noisier than the R180 it replaced. Remember the 280Z's and later cars had MUCH more deadening material over the diff area, and ZX's had a rubber isolated subframe! They also had fifth gear in most cases, keeping overall revs lower for the same speed.
Chances are, the noise is there above 80, it's just so loud in the 240, you can't hear it as much.
Takes a LOT of setup to get a quiet R-200, I just decided to live with it, as mine's solid-mounted anyway (as was the R180 it replaced)...