I think I have the same thing as well.. I got the issue when the local Indy changed the oil in the Transfer Case. I think they used the oil for the pre facelift, not the later like my 2005.

Do you get it when you are cruising, like a steady speed but just holding the throttle to keep that speed?

I have been trying to record it, but my recorder wont pick it up properly in the car. I'm going to have to put the recorder under the car somewhere and go for drives until it happens.

Rob