During testing on a small gas turbine, frequencies related to the power turbine shaft and a bearing were observed. The frequencies of the fault were not associated with any known bearing on the power turbine shaft. This paper is an investigation of why the observed bearing fault frequency of 6% higher than anticipated. It will be shown that because the faulted bearing was a worn thrust bearing, the contact angle and pitch diameter of the roller element had changed. This is an infrequently observed phenomenon, which can lead to missed fault detection on a critical component. A mitigation strategy for this type of failure is discussed.