Tires: tire noise in left front tire, goodyear wrangler, cv joints

Question
I have a Jeep Wrangler that has developed a noise in just the left front tire.  The tires are Goodyear Wrangler GS-A that were purchased 4 years ago to replace existing.  The tires have even wear and are keep properly inflated but have not been rotated.  They have performed well in all conditions and we especially like their traction in snow/ice/mud. They have about 27,000 miles on them and remaining tread looks good to me.  I noticed the noise about three months ago when the jeep's windows were out.  It is a "thuk-thuk" noise that is now audible from 35 mph and higher.  It started out as audible only between 45-55 mph.  The noise is proportional to speed.  The faster we are going the faster the "thuk-thuk" noise.  It sounds very much like something embedded in the tire that hits the road each time it goes around.  But, the tire surfacr is clear.  I even picked every small stone out of the groves and the noise remains the same.  We have checked with local dealers and the answers have ranged from broken belt to defective strut.  The struts, wheel and jeep suspension look good to our trusted local mechanic, but he is not a tire guy.  Any thoughts?

Answer
Dirk,

A little diagnostic work will really help here.

Rotate your tires.  

If the noise moves, it's the tires.  If so, it's probably an alignment induced wear issue.  Even though it may not seem like there is a wear problem, it doesn't take much variation in tread wear to produce noise.

But if it doesn't move, then it's something rotating - brakes, CV joints, something like that.