I notice on my TX 2 that when the arm is moving across the record it makes a thud sound that I pick up in my speakers. While music is playing its to quiet, but you notice it the most when it is in between songs. I would say the sound occurs every sec or so. What could be the cause of that sound?

Does the sound interval match the revs of the platter? If the platter height adjustment is not quite right, the underside of it might rub the belt or something else and make the sound.

Another thing that obviously moves about once a second is the arm itself. I can't think of any reason why the servo that moves it could cause any sound, though - unless the tracks are dirty and sticky, perhaps?

It seems like a platter adjustment, how would be a way to change the height?

Under the platter there are 3 equidistant copper leaf springs with adjustment screws at the ends furthest away from the platter. Screw them down and they lift the platter height at that point.

Chris.