My service advisor called me today saying a new TSB was sent to him this morning which addresses this issue.

TSB: 641805

This TSB addresses the transmission-whine-sounds that come into the cabin while under power. The problem is an evaporator hose that exits next to the transmission. A two-way valve opens whenever the fan runs on the climate control system, thus allowing sounds to be transmitted up the hose and into the cabin. Solution: Install a one-way valve with the part indicated in the TSB.

I plan to have mine done in the next couple of days and will report the success of this procedure. I can consistently repeat the problem so I'll very quickly know if it worked or not.

Chris