An experimental study of an active shaft transverse vibration control system for suppressing gear mesh vibratory response due to transmission error excitation in a high power density gearbox is presented. The proposed active control concept employs a piezoelectric stack actuator to deliver the control force through a secondary bearing. A versatile test stand that includes a closed-loop, power recirculating, dual-gearbox set-up capable of high load transfer is specially designed for this work. The underlying controller for computing the actuation signal is based on a modified filtered-x LMS algorithm with a robust frequency estimation technique. In order to avoid the common out-of-band overshoot problem, an integrated adaptive linear enhancer is also applied. Both single mesh frequency and multi-harmonic control cases are examined to evaluate the performance of the active control system. Additionally, the impact of the adaptive linear enhancer order as well as the controller adaptation step size on active control performance is evaluated. The experiments performed show more than 10 dB reduction in housing vibrations at certain targeted mesh harmonics over a range of operating speeds.