ESA's XMM-Newton space observatory, the flagship of European X-ray astronomy, is after it's launch in 1999 the most powerful X-ray telescope ever placed in orbit. The mission originally designed for a 10 years lifetime is planned to be operated long into this decade since spacecraft and instruments are operating admirably without major degradation. Therefore recently a system called XMM Early Warning System (XEWS) is developed to perform near-real-time trend analysis of spacecraft parameters in order to detect early degradation of components. This will enable the mission to perform early counter measures in case degradation is detected. During the development of XEWS it has been spotted that one of XMM-Newton's reaction wheels shows since 2008 non-periodic friction increase during stable pointing. We present an analysis of all four reactions wheels since the start of the mission identifying the periods of increased friction and giving some possible causes and cures for this effect that is as well know as "cage instability" and describe the impact on operations. Additionally a comparison with the wheels of ESA's INTEGRAL spacecraft which is using effectively the same Attitude and Orbit Control System will be presented..