No seams in the tubes I have. They are molded in one piece. There a lines in them which are parting lines for the mold segments. Cut a tube open and you'll see there are no internal lines or seams.

Small longitudinal cuts on the sides of the tubes can be due to pinch flats, where the tire is compressed by a sharp edge in the pavement or an object far enough that the tube gets trapped and pinched. Depending on the conditions where you ride, how you ride, and the tire pressure, these can be relatively common.