I have an '06 DTS. There is a front end vibration. Vibration at all speeds. It is barely noticeable at lower speeds, but it gets more prominent at higher speeds. I have heard that this is common in an '09 DTS. Does anyone have any knowledge about this problem.

 

Front end vibrations are not normal, doesn't matter if they are common.

Some reasons for a front end vibration could be an out of balance wheel, loose or worn wheel bearings, worn tie rod ends, worn ball joints, centre wear on steering rack, bad tires with split belts or blisters, warped brake rotors.

Going by the age of your car I'd start with a tire roation and see what happens, next I'd go to the brake rotors, probably need a brake job anyway by now.