What's broke?

Have you checked the shifter body and linkage to make sure something isn't loose there?

Yes. Everything there is snug...complete with proper spring clips on the shifter rod ends.

This noise is not of an external nature. There is a 'depth' to the noise. It seems to be coming from inside the trans.

I did recently replace the OEM crossmember mount with a poly-bushed version. That could well account for the 'newness' of the noise to me. Replacement of that mount did not coincide with noticing the vibration part though.

In anticipation of any who would say, 'How could you take out the mushy-old rubber mount, put in a new poly mount and not notice a difference in feel?' I'm not saying that. There was a difference in feel...but it's not that vibration that's part of this matter.