Tires: Bump, Tire Noise

Question
I assume this is a tire problem---not sure. I have noticed a constant "bump-bump bump" when my 2004 Lexus LS 430 is at speed, frequency proportional to speed. Its present if car is in gear or neutral, not loud but ever present. Tires are Dunlop SP 5000s, with about 16K miles on them.
I would appreciate any suggestions. Thanks so much.

Answer
Keefe,

See if you can determine what corner it is coming from - at the very least whether it is front or back.

Then swap the front tires with the rears.

Did the noise move?  

If not, then the problem is in the vehicle - likely CV joints.

If so, then it is likely irregular tire wear.  Irregular wear is caused by misalignment and aggravated by insufficient inflation pressure and insufficient rotation practices.  So an alignment is needed.  The alignment won't fix the wear that is already there, but it will prevent it from becoming worse.  The only fix for irregular wear is to either be patient and hope a new wear pattern developes or to buy new tires.