This problems was not noticed during the test drive. After several weeks it was noticed while driving more slowly through residential streets. At first it was assumed to be road noise.

While traveling between 25-30 mph a whining sound is heard from the engine compartment. Release the accelerator and the whining appears to be gone. It also appears to be gone above 30 mph however, very prevalent in the mph mentioned. A dealership mechanic rode with me and thought that the problem to be the "intake manifold turbulence". I drove a 2009 DTS and the same condition exist. This was brought to the attention of Cadillac and their conclusion was "it's a natural characteristic of the DTS". It is annoying, particularly from a Cadillac, for that matter, any new vehicle. Cadillac declined to make a fix on this complaint.