A tubing string, such as a coiled tubing or jointed tubing string, has an agitator mounted within an interior of the tubing string at an intermediate position between an uphole end and a downhole end of the tubing string. A tubing agitator is structured to be installed within a tubing string. A method includes: forming or installing a seat within an interior of a tubing string at an intermediate position between an uphole end and a downhole end of the tubing string; and conveying an agitator through the interior of the tubing string until the agitator contacts the seat. A hammer drift tool is also described.