RF MEMS switches have become a popular choice for reconfigurable circuits due to their high performance. MEMS switch banks, phase shifters and tunable filters developed over the last decade show promise in realizing miniature reconfigurable radios of tomorrow. However, as devices are scaled to the micro-regime, thermal fluctuations in MEMS structures manifest themselves as phase noise at the output of the MEMS devices and circuits, potentially limiting their performance. This presentation discusses the non-linear effects of Brownian motion on MEMS switches, resonators and tunable filters. Mechanical instabilities in the MEMS structure when operated at high power, makes a MEMS device more vulnerable to phase noise. An insight into the effect of filter parameters on the phase noise of a MEMS tunable filter will also be provided. Non-linear noise analysis in all-pole tunable filters will be discussed in the context of a general approach to model power-dependent noise phenomenon in reconfigurable MEMS filters.