Over the past decade we have been able to vastly improve the control algorithms of our biped walking robot LOLA. Further enhancements, however, are limited by vibration problems caused by the dynamics of LOLA's mechanical structure. In this work, we present small examples how structural dynamics limit our control design for walking control as well as low level position control of the joints. We also provide a procedure to identify weaknesses in the structural design of our biped using Experimental Modal Analysis. Using this method, we could successfully identify the structural modes of the system. Furthermore, we were able to use a closed-loop identification method to show a connection between the control loop resonances and the structural resonances of our robot.