Yep. That was me who had the whistling sound. My MY05 4.4 had a black condensation drain tube which connected into the vent system and exited down by the transmission. The result: whenever my fan was on at any speed I heard a whistling sound coming out of my vents. That whistling sound was actually the normal whine of my transmission being heard through my vents. If you turn your climate control system fully off and it goes away, then that's what your problem is.

The fix: A new drain hose design avail from your dealer which has a slit for an opening. When water collects at the bottom, the weight of the water opens the slit and it drains out. But no sounds are allowed back up into the black drain tube.

Hope this helps.

Chris