GS Intermittent Shudder when accelerating.

[DonGS300]

My 2006 GS300 has developed a shudder about 10% of the time when I am accelerating normally (at about 30 MPH).  It goes away when I accelerate to a higher speed.  Everything else is normal, at any speed.  The service man at the dealer test drove it, and says everything seems OK.  Of course, it didn't do it for him.  It doesn't seem to be the transmission, because it is only at this one load point when I am accelerating, and it is intermittent.    Any idea what this could be?   Is this how a wheel bearing would fail?